Align IA32_ARCH_CAP MSR definitions and use with SDM rev. 068.

SDM rev. 068 was released yesterday and it contains the description of
the MSR 0x10a IA32_ARCH_CAP. This change adds symbolic definitions for
all bits present in the document, and decode them in the CPU
identification lines printed on boot.

But also, the document defines SSB_NO as bit 4, while FreeBSD used but
2 to detect the need to work-around Speculative Store Bypass
issue.  Change code to use the bit from SDM.

Similarly, the document describes bit 3 as an indicator that L1TF
issue is not present, in particular, no L1D flush is needed on
VMENTRY.  We used RDCL_NO to avoid flushing, and again I changed the
code to follow new spec from SDM.

In fact my Apollo Lake machine with latest ucode shows this:
    IA32_ARCH_CAPS=0x19<RDCL_NO,SKIP_L1DFL_VME,SSB_NO>

Reviewed by:	bwidawsk
Sponsored by:	The FreeBSD Foundation
MFC after:	3 days
Differential revision:	https://reviews.freebsd.org/D18006

sys/amd64/vmm/intel/vmx.c

@@ -814,7 +814,8 @@ vmx_init(int ipinum)
 		return (error);
 	}
 
-	guest_l1d_flush = (cpu_ia32_arch_caps & IA32_ARCH_CAP_RDCL_NO) == 0;
+	guest_l1d_flush = (cpu_ia32_arch_caps &
+	    IA32_ARCH_CAP_SKIP_L1DFL_VMENTRY) == 0;
 	TUNABLE_INT_FETCH("hw.vmm.l1d_flush", &guest_l1d_flush);
 
 	/*

sys/x86/include/specialreg.h

@@ -434,7 +434,9 @@
 /* MSR IA32_ARCH_CAP(ABILITIES) bits */
 #define	IA32_ARCH_CAP_RDCL_NO	0x00000001
 #define	IA32_ARCH_CAP_IBRS_ALL	0x00000002
-#define	IA32_ARCH_CAP_SSBD_NO	0x00000004
+#define	IA32_ARCH_CAP_RSBA	0x00000004
+#define	IA32_ARCH_CAP_SKIP_L1DFL_VMENTRY	0x00000008
+#define	IA32_ARCH_CAP_SSB_NO	0x00000010
 
 /*
  * CPUID manufacturers identifiers

sys/x86/x86/cpu_machdep.c

@@ -891,7 +891,7 @@ hw_ssb_recalculate(bool all_cpus)
 		hw_ssb_set(true, all_cpus);
 		break;
 	case 2: /* auto */
-		hw_ssb_set((cpu_ia32_arch_caps & IA32_ARCH_CAP_SSBD_NO) != 0 ?
+		hw_ssb_set((cpu_ia32_arch_caps & IA32_ARCH_CAP_SSB_NO) != 0 ?
 		    false : true, all_cpus);
 		break;
 	}

sys/x86/x86/identcpu.c

@@ -1014,6 +1014,9 @@ printcpuinfo(void)
 				       "\020"
 				       "\001RDCL_NO"
 				       "\002IBRS_ALL"
+				       "\003RSBA"
+				       "\004SKIP_L1DFL_VME"
+				       "\005SSB_NO"
 				       );
 			}