Remove all kernel uses of pcb_psl, but keep in in the struct to

preserve the ABI and API for applications.  It was removed in the port
to amd64, but was remained as garbage giving a micro-pessimization and
spurious single-step traps on i386.

pcb_psl was intended to be used just to do a context switch of PSL_I,
but this context switch was null in most or all versions, and
mis-switching of PSL_T was done instead.

Some history:
- in 386BSD-0.0, cpu_switch() ran at splhigh() and splhigh() did too
  much interrupt disabling, so interrupts were hard-disabled across
  cpu_switch() and too many other places
- in 386BSD-0.0-patchkit through FreeBSD-4 and FreeBSD-5 before
  SMPng, splhigh() did soft interrupt masking, and cpu_switch() was
  excessively cautious and did a cli at the start and a sti at the
  end to hard-disable interrupts across the switch
- SMPng replaced the spl's and cli's by spinlocks (just sched_lock?),
  so interrupts were hard-disabled across cpu_switch() and too many
  other places again
- initial attempts to fix this intended to restore some soft
  interrupt disabling, but to support variations in this cpu_switch()
  used pushfl/popfl into pcb_psl to avoid hard-coding the assumption
  that the initial and final states have PSL_I enabled.  But the
  version with soft interrupt disabling wasn't used for long, or was
  never committed, (except I always used my different version of it
  for UP) so the pushfl/popl and pcb_psl to hold them have been doing
  less than nothing for about 14 years.

sys/i386/i386/genassym.c

@@ -143,7 +143,6 @@ ASSYM(PCB_DR2, offsetof(struct pcb, pcb_dr2));
 ASSYM(PCB_DR3, offsetof(struct pcb, pcb_dr3));
 ASSYM(PCB_DR6, offsetof(struct pcb, pcb_dr6));
 ASSYM(PCB_DR7, offsetof(struct pcb, pcb_dr7));
-ASSYM(PCB_PSL, offsetof(struct pcb, pcb_psl));
 ASSYM(PCB_DBREGS, PCB_DBREGS);
 ASSYM(PCB_EXT, offsetof(struct pcb, pcb_ext));
 

sys/i386/i386/swtch.s

@@ -131,8 +131,6 @@ ENTRY(cpu_switch)
 	movl	%esi,PCB_ESI(%edx)
 	movl	%edi,PCB_EDI(%edx)
 	mov	%gs,PCB_GS(%edx)
-	pushfl					/* PSL */
-	popl	PCB_PSL(%edx)
 	/* Test if debug registers should be saved. */
 	testl	$PCB_DBREGS,PCB_FLAGS(%edx)
 	jz      1f                              /* no, skip over */
@@ -261,8 +259,6 @@ sw1:
 	movl	PCB_EDI(%edx),%edi
 	movl	PCB_EIP(%edx),%eax
 	movl	%eax,(%esp)
-	pushl	PCB_PSL(%edx)
-	popfl
 
 	movl	%edx, PCPU(CURPCB)
 	movl	TD_TID(%ecx),%eax
@@ -365,8 +361,6 @@ ENTRY(savectx)
 	movl	%esi,PCB_ESI(%ecx)
 	movl	%edi,PCB_EDI(%ecx)
 	mov	%gs,PCB_GS(%ecx)
-	pushfl
-	popl	PCB_PSL(%ecx)
 
 	movl	%cr0,%eax
 	movl	%eax,PCB_CR0(%ecx)

sys/i386/i386/vm_machdep.c

@@ -273,7 +273,6 @@ cpu_fork(td1, p2, td2, flags)
 	pcb2->pcb_esp = (int)td2->td_frame - sizeof(void *);
 	pcb2->pcb_ebx = (int)td2;		/* fork_trampoline argument */
 	pcb2->pcb_eip = (int)fork_trampoline;
-	pcb2->pcb_psl = PSL_KERNEL;		/* ints disabled */
 	/*-
 	 * pcb2->pcb_dr*:	cloned above.
 	 * pcb2->pcb_savefpu:	cloned above.
@@ -504,7 +503,6 @@ cpu_copy_thread(struct thread *td, struct thread *td0)
 	pcb2->pcb_esp = (int)td->td_frame - sizeof(void *); /* trampoline arg */
 	pcb2->pcb_ebx = (int)td;			    /* trampoline arg */
 	pcb2->pcb_eip = (int)fork_trampoline;
-	pcb2->pcb_psl &= ~(PSL_I);	/* interrupts must be disabled */
 	pcb2->pcb_gs = rgs();
 	/*
 	 * If we didn't copy the pcb, we'd need to do the following registers:

sys/i386/include/pcb.h

@@ -89,7 +89,7 @@ struct pcb {
 
 	caddr_t	pcb_onfault;	/* copyin/out fault recovery */
 	struct	pcb_ext	*pcb_ext;	/* optional pcb extension */
-	int	pcb_psl;	/* process status long */
+	int	pcb_waspsl;	/* unused padding for ABI and API compat */
 	u_long	pcb_vm86[2];	/* vm86bios scratch space */
 	union	savefpu *pcb_save;