ARM: OMAP: Implement workaround for GPIO wakeup bug in OMAP2420 silicon

Some GPIOs on OMAP2420 do not have wakeup capabilities. If these GPIOs
are configured as IRQ sources, spurious interrupts will be generated
each time the core domain enters retention.

Signed-off-by: Juha Yrjola <juha.yrjola@solidboot.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>