[ARM] pxa: program MFPs for low power mode when suspending

Hook the MFP code into the power management code so that the MFPs can
be reconfigured when suspending and resuming.  However, note the FIXME
- low power mode MFP configuration may depend on the system state being
entered.

Also note that we have to clear any detected edge events prior to
entering a low power mode - otherwise we immediately wake up.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>