PPC: Depend behavior of cmp instructions only on instruction encoding

PPC: Depend behavior of cmp instructions only on instruction encoding

When running an L=1 cmp instruction on a 64bit PPC CPU with SF off, it
still behaves identical to what it does when SF is on. Remove the implicit
difference in the code.

Also, on most 32bit CPUs we should always treat the compare as 32bit
compare, as the CPU will ignore the L bit. This is not true for e500mc,
but that's up for a different patch.

Reported-by: Torbjorn Granlund <tg@gmplib.org>
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Alexander Graf <agraf@suse.de>