regmap: add force_write option on _regmap_update_bits()

Sometimes we want to write data even though it doesn't change value.
Then, force_write option on _regmap_update_bits() helps this purpose.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Mark Brown <broonie@kernel.org>