OMAP3: PM: PRCM interrupt: check MPUGRPSEL register

PM_WKST register contents should be ANDed with the contents of the
MPUGRPSEL registers.  Otherwise the MPU PRCM interrupt handler could
wind up clearing wakeup events meant for the IVA PRCM interrupt
handler. A future revision to this code should be to read a cached
version of MPUGRPSEL from the powerdomain code, since PRM reads are
relatively slow.

Updated after Jon Hunter's PRCM IRQ change by Kevin Hilman

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>