regmap: add regmap_fields_force_write()

regmap_fields_force_write() is similar to regmap_fields_write(),
but regmap_fields_force_write() write data to register even though
it is same value.

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