ARM: 7914/1: amba: Drop legacy PM support and use the pm_generic functions

All AMBA drivers have converted to use the modern PM ops thus we can
safely drop the legacy PM support from the bus.

While using the modern PM ops it also makes sense to convert to use the
pm_generic callback functions.

Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>