arch-power: Fix branch instructions

arch-power: Fix branch instructions

This fixes the following branch instructions in order to
support 64-bit addressing:
  * Branch (b[l][a])
  * Branch Conditional (bc[l][a])
  * Branch Conditional to Link Register (bclr[l])
  * Branch Conditional to Count Register (bcctr[l])

This also fixes disassembly generation for all of the above.

Change-Id: I7cad4e1b3b2945ab06c4ffc8c79842f1453c85ec
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>