powerpc: Convert cmp to cmpd in idle enter sequence

commit 80f23935 upstream.

PowerPC's "cmp" instruction has four operands. Normally people write
"cmpw" or "cmpd" for the second cmp operand 0 or 1. But, frequently
people forget, and write "cmp" with just three operands.

With older binutils this is silently accepted as if this was "cmpw",
while often "cmpd" is wanted. With newer binutils GAS will complain
about this for 64-bit code. For 32-bit code it still silently assumes
"cmpw" is what is meant.

In this instance the code comes directly from ISA v2.07, including the
cmp, but cmpd is correct. Backport to stable so that new toolchains can
build old kernels.

Fixes: 948cf67c ("powerpc: Add NAP mode support on Power7 in HV mode")
Reviewed-by: Vaidyanathan Srinivasan <svaidy@linux.vnet.ibm.com>
Signed-off-by: Segher Boessenkool <segher@kernel.crashing.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
[bwh: Backported to 3.2: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>

arch/powerpc/kernel/idle_power7.S

@@ -67,7 +67,7 @@ _GLOBAL(power7_idle)
 	std	r0,0(r1)
 	ptesync
 	ld	r0,0(r1)
-1:	cmp	cr0,r0,r0
+1:	cmpd	cr0,r0,r0
 	bne	1b
 	PPC_NAP
 	b	.