[ARM] pxa: add muxed gpio wakeup sources on pxa2xx architectures

PXA SoC have several GPIOs muxed on only one wakeup source.
Add support for these wakeup sources which were missing
in mfp core support.

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Eric Miao <eric.miao@marvell.com>