arch-power: Simplify doubleword operand types

arch-power: Simplify doubleword operand types

Currently, 'sq' and 'uq' are used to represent signed and
unsigned doublewords respectively. Since all recent Power
ISA specifications list 128-bit quadwords as a valid data
type, it may be misleading to use the current terminology
in case support for such operands are added in the future.
So, to simplify this, 'sd' and 'ud' are used to represent
signed and unsigned doublewords respectively.

Change-Id: Ie7831c596fc8f9ddfdf3b652c37cfe26484ebe01
Signed-off-by: Sandipan Das <sandipan@linux.vnet.ibm.com>