Correct ppc popcntb logic, implement popcntw and popcntd

Correct ppc popcntb logic, implement popcntw and popcntd

qemu already includes support for the popcntb instruction introduced
in POWER5 (although it doesn't actually allow you to choose POWER5).

However, the logic is slightly incorrect: it will generate results
truncated to 32-bits when the CPU is in 32-bit mode.  This is not
normal for powerpc - generally arithmetic instructions on a 64-bit
powerpc cpu will generate full 64 bit results, it's just that only the
low 32 bits will be significant for condition codes.

This patch corrects this nit, which actually simplifies the code slightly.

In addition, this patch implements the popcntw and popcntd
instructions added in POWER7, in preparation for allowing POWER7 as an
emulated CPU.

Signed-off-by: David Gibson <dwg@au1.ibm.com>
Signed-off-by: Alexander Graf <agraf@suse.de>