arch-power: Fix fixed-point compare instructions

arch-power: Fix fixed-point compare instructions

This fixes the following compare instructions:
  * Compare (cmp)
  * Compare Logical (cmpl)
  * Compare Immediate (cmpi)
  * Compare Logical Immediate (cmpli)

Instead of always doing a 32-bit comparison, these instructions
now use the length field to determine the type of comparison to
be done. The comparison can either be based on the lower order
32 bits or on all 64 bits of the values.

This also fixes disassembly generation for all of the above.

Change-Id: I6a9f783efa9ef2f2ef3c16eada61074d6f798a20
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>