soundwire: fix regmap dependencies and align with other serial links

The existing code has a mixed select/depend usage which makes no sense.

config SOUNDWIRE_BUS
       tristate
       select REGMAP_SOUNDWIRE

config REGMAP_SOUNDWIRE
        tristate
        depends on SOUNDWIRE_BUS

Let's remove one layer of Kconfig definitions and align with the
solutions used by all other serial links.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/20190718230215.18675-1-pierre-louis.bossart@linux.intel.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>