gpio: mt7621: add BGPIOF_NO_SET_ON_INPUT flag

DSET/DCLR registers only works on output pins. Add corresponding
BGPIOF_NO_SET_ON_INPUT flag to bgpio_init call to fix direction_out
behavior.

Signed-off-by: Chuanhong Guo <gch981213@gmail.com>
Tested-by: René van Dorst <opensource@vdorst.com>
Reviewed-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>