[ARM] pxa: use new pin configuration mechanism for mainstone

1. the following code to configure PGSRx is no way portable and
   intuitive:

-	PGSR0 = 0x00008800;
-       PGSR1 = 0x00000002;
-       PGSR2 = 0x0001FC00;
-       PGSR3 = 0x00001F81;

   this is removed as low power state has already been encoded in
   the pin configuration definitions.

   Note: there is no specific reason for some of the GPIOs to drive
   high in low power mode as indicated by the above setting, those
   bits are ignored, and the result is validated to work.

2. the following code to configure GPIO wakeup is removed as this
   is now totally handled by pxa2xx_mfp_config():

-       PWER  = 0xC0000002;
-       PRER  = 0x00000002;
-       PFER  = 0x00000002;

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