soundwire: Avoid runtime suspend after device path bringup

There is a possible race condition that runtime suspend is being
called after device path bringup. To avoid this race condition,
add a mutex lock during device path bringup to serialize runtime
suspend and resume.

CRs-Fixed: 967442
Change-Id: I268a25b05799c66fc019e19e46939286e54fb514
Signed-off-by: Sudheer Papothi <spapothi@codeaurora.org>