MFD: ucb1x00-core: add wakeup support

Add genirq wakeup support for the ucb1x00 device.  This allows an
attached gpio_keys driver to wakeup the system.  Touchscreen is also
possible.

When there are no wakeup sources, ask the platform to assert the reset
signal to avoid any unexpected behaviour; this also puts the reset
signal at the right level when power is removed from the device.

Acked-by: Jochen Friedrich <jochen@scram.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>