powerpc: Fix building of feature-fixup tests on ppc32

We need to use PPC_LCMPI otherwise we get compile errors like:

arch/powerpc/lib/feature-fixups-test.S: Assembler messages:
arch/powerpc/lib/feature-fixups-test.S:142: Error: Unrecognized opcode: `cmpdi'
arch/powerpc/lib/feature-fixups-test.S:149: Error: Unrecognized opcode: `cmpdi'
arch/powerpc/lib/feature-fixups-test.S:164: Error: Unrecognized opcode: `cmpdi'

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>