Save are floating point state in cpu_switch() if needed instead of relying

completely on lazy floating point state saving.  This is needed for the
SMP case since processes can migrate to other CPUs.

Submitted by:	dfr

sys/alpha/alpha/machdep.c

@@ -2131,7 +2131,7 @@ alpha_fpstate_save(struct proc *p, int write)
 	critical_t s;
 
 	s = critical_enter();
-	if (p == PCPU_GET(fpcurproc)) {
+	if (p != NULL && p == PCPU_GET(fpcurproc)) {
 		/*
 		 * If curproc != fpcurproc, then we need to enable FEN 
 		 * so that we can dump the fp state.

sys/alpha/alpha/swtch.s

@@ -140,6 +140,13 @@ Lcs1:	LDGP(pv)
 	cmpeq	s0, s2, t0			/* oldproc == newproc? */
 	bne	t0, Lcs7			/* Yes!  Skip! */
 
+	/*
+	 * Save fp state if we have some.
+	 */
+	mov	s0, a0				/* curproc */
+	ldiq	a1, 1				/* clear fpcurproc */
+	CALL(alpha_fpstate_save)
+
 	/*
 	 * Deactivate the old address space before activating the
 	 * new one.  We need to do this before activating the