powerpc: Disable interrupts in 64-bit kernel FP and vector faults

If we get a floating point, altivec or vsx unavaible interrupt in
kernel, we trigger a kernel error. There is no point preserving
the interrupt state, in fact, that can even make debugging harder
as the processor state might change (we may even preempt) between
taking the exception and landing in a debugger.

So just make those 3 disable interrupts unconditionally.

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
---

v2: On BookE only disable when hitting the kernel unavailable
    path, otherwise it will fail to restore softe as
    fast_exception_return doesn't do it.
diff --git a/arch/powerpc/kernel/exceptions-64s.S b/arch/powerpc/kernel/exceptions-64s.S
index d8ff6d3..0fb42ae 100644
--- a/arch/powerpc/kernel/exceptions-64s.S
+++ b/arch/powerpc/kernel/exceptions-64s.S
@@ -762,8 +762,8 @@
 	EXCEPTION_PROLOG_COMMON(0x800, PACA_EXGEN)
 	bne	1f			/* if from user, just load it up */
 	bl	.save_nvgprs
+	DISABLE_INTS
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	ENABLE_INTS
 	bl	.kernel_fp_unavailable_exception
 	BUG_OPCODE
 1:	bl	.load_up_fpu
@@ -782,8 +782,8 @@
 END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
 #endif
 	bl	.save_nvgprs
+	DISABLE_INTS
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	ENABLE_INTS
 	bl	.altivec_unavailable_exception
 	b	.ret_from_except
 
@@ -798,8 +798,8 @@
 END_FTR_SECTION_IFSET(CPU_FTR_VSX)
 #endif
 	bl	.save_nvgprs
+	DISABLE_INTS
 	addi	r3,r1,STACK_FRAME_OVERHEAD
-	ENABLE_INTS
 	bl	.vsx_unavailable_exception
 	b	.ret_from_except