gpio/omap: use pm-runtime framework

Call runtime pm APIs pm_runtime_get_sync() and pm_runtime_put()
for enabling/disabling clocks appropriately. Remove syscore_ops and
instead use SET_RUNTIME_PM_OPS macro.

There is no more need to call omap_device_disable_idle_on_suspend
since driver is PM runtime adapted now.

Signed-off-by: Charulatha V <charu@ti.com>
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>