[SPARC64]: Kill all %pstate changes in context switch code.

They are totally unnecessary because:

1) Interrupts are already disabled when switch_to()
   runs.

2) We don't use hard-coded alternate globals any longer.

This found a case in rtrap, which still assumed alternate
global %g6 was current_thread_info(), and that is fixed
by this changeset as well.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

arch/sparc64/kernel/rtrap.S

@@ -224,7 +224,8 @@ rt_continue:	ldx			[%sp + PTREGS_OFF + PT_V9_G1], %g1
 		ldx			[%sp + PTREGS_OFF + PT_V9_G4], %g4
 		ldx			[%sp + PTREGS_OFF + PT_V9_G5], %g5
 		brz,pt			%l3, 1f
-		 nop
+		mov			%g6, %l2
+
 		/* Must do this before thread reg is clobbered below.  */
 		LOAD_PER_CPU_BASE(%g5, %g6, %i0, %i1, %i2)
 1:
@@ -238,6 +239,8 @@ rt_continue:	ldx			[%sp + PTREGS_OFF + PT_V9_G1], %g1
 		SET_GL(1)
 		.previous
 
+		mov			%l2, %g6
+
 		ldx			[%sp + PTREGS_OFF + PT_V9_I0], %i0
 		ldx			[%sp + PTREGS_OFF + PT_V9_I1], %i1
 

include/asm-sparc64/system.h

@@ -213,7 +213,6 @@ do {	if (test_thread_flag(TIF_PERFCTR)) {				\
 		task_thread_info(next);					\
 	__asm__ __volatile__(						\
 	"mov	%%g4, %%g7\n\t"						\
-	"wrpr	%%g0, 0x95, %%pstate\n\t"				\
 	"stx	%%i6, [%%sp + 2047 + 0x70]\n\t"				\
 	"stx	%%i7, [%%sp + 2047 + 0x78]\n\t"				\
 	"rdpr	%%wstate, %%o5\n\t"					\
@@ -227,14 +226,10 @@ do {	if (test_thread_flag(TIF_PERFCTR)) {				\
 	"ldx	[%%g6 + %3], %%o6\n\t"					\
 	"ldub	[%%g6 + %2], %%o5\n\t"					\
 	"ldub	[%%g6 + %4], %%o7\n\t"					\
-	"mov	%%g6, %%l2\n\t"						\
 	"wrpr	%%o5, 0x0, %%wstate\n\t"				\
 	"ldx	[%%sp + 2047 + 0x70], %%i6\n\t"				\
 	"ldx	[%%sp + 2047 + 0x78], %%i7\n\t"				\
-	"wrpr	%%g0, 0x94, %%pstate\n\t"				\
-	"mov	%%l2, %%g6\n\t"						\
 	"ldx	[%%g6 + %6], %%g4\n\t"					\
-	"wrpr	%%g0, 0x96, %%pstate\n\t"				\
 	"brz,pt %%o7, 1f\n\t"						\
 	" mov	%%g7, %0\n\t"						\
 	"b,a ret_from_syscall\n\t"					\