ARM: 6758/1: amba: support pm ops

Support pm_ops in the AMBA bus, required to allow drivers to use runtime pm.
The implementation of AMBA bus pm ops is based on the platform bus
implementation.

Acked-by: Rafael J. Wysocki <rjw@sisk.pl>
Acked-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Rabin Vincent <rabin.vincent@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>