regmap: add regmap_write_bits()

regmap_write_bits() is similar to regmap_update_bits(),
but regmap_write_bits() 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>
(cherry picked from commit fd4b7286

)
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>