gpio/omap: fix incorrect access of debounce module

Enable debounce clock before writing/reading debounce registers.
Disable the clock at the end so that it is synchronized with the
pm_runtime_get/put_sync calls.

Enable debounce clock per module. This call is mandatory because
in omap_gpio_request() when *_runtime_get_sync() is called,
_gpio_dbck_enable() within runtime callbck fails to turn on dbck
 because dbck_enable_mask used within _gpio_dbck_enable() is still
not initialized at that point. Therefore we have to enable dbck here.

Signed-off-by: Tarun Kanti DebBarma <tarun.kanti@ti.com>
Reviewed-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Kevin Hilman <khilman@ti.com>