soundwire: bus_type: introduce sdw_slave_type and sdw_master_type

this is a preparatory patch before the introduction of the
sdw_master_type. The SoundWire slave support is slightly modified with
the use of a sdw_slave_type, and the uevent handling move to
slave.c (since it's not necessary for the master).

No functionality change other than moving code around.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Acked-by: Jaroslav Kysela <perex@perex.cz>
Link: https://lore.kernel.org/r/20200518174322.31561-3-yung-chuan.liao@linux.intel.com


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