arch-power: Add population count instructions

This adds the following instructions.
  * Population Count Bytes (popcntb)
  * Population Count Words (popcntw)
  * Population Count Doubleword (popcntd)

Change-Id: Id15188482b45552735c1d960418d5d6ba1f2ede8
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/40921
Reviewed-by: Boris Shingarov <shingarov@labware.com>
Maintainer: Boris Shingarov <shingarov@labware.com>
Tested-by: kokoro <noreply+kokoro@google.com>
1 file changed