ARM: 8361/1: sa1100: add platform functions to handle PWER settings

PWER settings logically belongs neither to GPIO nor to system IRQ code.
Add special functions to handle PWER (for GPIO and for system IRQs)
from platform code.

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>