arch-power: Add doubleword rotate instructions

arch-power: Add doubleword rotate instructions

This introduces a new class and a new format for MD and
MDS form instructions where the shift amount, mask begin
and mask end are specified by two fields that must be
concatenated and adds the following instructions.
  * Rotate Left Doubleword Immediate then Clear Left (rldicl[.])
  * Rotate Left Doubleword Immediate then Clear Right (rldicr[.])
  * Rotate Left Doubleword Immediate then Clear (rldic[.])
  * Rotate Left Doubleword then Clear Left (rldcl[.])
  * Rotate Left Doubleword then Clear Right (rldcr[.])
  * Rotate Left Doubleword Immediate then Mask Insert (rldimi[.])

Change-Id: Id7f1f24032242ccfdfda2f1aefd6fe9f0331f610
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>