arch-power: Fix move condition field instructions

arch-power: Fix move condition field instructions

This introduces the S field for X form instructions which
is used to specify signed versus unsigned comparison. The
Power ISA does not specify a formal name for the third
1-bit opcode field required for decoding XFX form move to
and from CR field instructions, the S field can be used
to achieve the same as it has the same span and position.
This fixes the following instructions.
  * Move To Condition Register Fields (mtcrf)
  * Move From Condition Register (mfcr)

Change-Id: I8d291f707cd063781f0497f7226bebfc47bd9e63
Signed-off-by: Sandipan Das <sandipan@linux.ibm.com>