regmap: add regmap_fields_update_bits_base()

This patch adds new regmap_fields_update_bits_base() which is using
regmap_update_bits_base().
Current regmap_fields_xxx() can be merged into it by macro.

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