ARM: OMAP: GPIO: IRQSTATUS2 workaround for retention state

In OMAP2420, an incoming GPIO interrupt always sets both GPIO_IRQSTATUS1
and GPIO_IRQSTATUS2, even if the relevant bit is disabled in
GPIO_IRQENABLE1/2 and DSP doesn't use GPIO at all. GPIO_IRQSTATUS1
is for MPU and GPIO_IRQSTATUS2 is for DSP. If IRQSTATUS is set, this
will prevent the system from going to idle state. This patch also clears
IRQSTATUS2 to avoid the above situation.

Signed-off-by: Hiroshi DOYU <Hiroshi.DOYU@nokia.com>
Signed-off-by: Juha Yrjola <juha.yrjola@solidboot.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>