arch-power: Fix fixed-point word rotate instructions

arch-power: Fix fixed-point word rotate instructions

This fixes the following rotate instructions:
  * Rotate Left Word Immediate then And with Mask (rlwinm[.])
  * Rotate Left Word then And with Mask (rlwnm[.])
  * Rotate Left Word Immediate then Mask Insert (rlwimi[.])

For 64-bit execution, these instructions should perform rotate
operations on a 64-bit value formed by concatenating two copies
of the lower order 32 bits of the value in the source register.

This also fixes disassembly generation for all of the above.

Change-Id: Iccd8c6ad10a26d66dcecd64c8f1f8118ec8c1278
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>