ARM: OMAP2+: gpmc: Converts GPMC driver to pm_runtime capable

Support for pm_runtime add to GPMC driver.

Signed-off-by: Philip Avinash <avinashphilip@ti.com>
Signed-off-by: Pekon Gupta <pekon@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>