[ARM] pxa: allow dynamic enable/disable of GPIO wakeup for pxa{25x,27x}

[ARM] pxa: allow dynamic enable/disable of GPIO wakeup for pxa{25x,27x}

Changes include:

1. rename MFP_LPM_WAKEUP_ENABLE into MFP_LPM_CAN_WAKEUP to indicate
   the board capability of this pin to wakeup the system

2. add gpio_set_wake() and keypad_set_wake() to allow dynamically
   enable/disable wakeup from GPIOs and keypad GPIO

   * these functions are currently kept in mfp-pxa2xx.c due to their
     dependency to the MFP configuration

3. pxa2xx_mfp_config() only gives early warning if MFP_LPM_CAN_WAKEUP
   is set on incorrect pins

So that the GPIO's wakeup capability is now decided by the following:

   a) processor's capability: (only those GPIOs which have dedicated
      bits within PWER/PRER/PFER can wakeup the system), this is
      initialized by pxa{25x,27x}_init_mfp()

   b) board design decides:
      - whether the pin is designed to wakeup the system (some of
        the GPIOs are configured as other functions, which is not
        intended to be a wakeup source), by OR'ing the pin config
        with MFP_LPM_CAN_WAKEUP

      - which edge the pin is designed to wakeup the system, this
        may depends on external peripherals/connections, which is
        totally board specific; this is indicated by MFP_LPM_EDGE_*

   c) the corresponding device's (most likely the gpio_keys.c) wakeup
      attribute:

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