soundwire: intel: introduce helpers to start bus

There are 3 different sequences to start the bus, let's move the
functionality to helpers.

There should be no functionality change, except in error cases where
the flow is improved with more consistent disabling of interrupts and
powering down.

Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Reviewed-by: Rander Wang <rander.wang@intel.com>
Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
Link: https://lore.kernel.org/r/20220919175721.354679-11-yung-chuan.liao@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>