ASoC: wcd-dsp-mgr: fix race during subsystem restart

Whenever subsystem restart or DSP boot occurs, the manager driver
parses the dsp image and stores the segments in list. During
certain back to back regression tests, it is observed that SSR
is failing due to race between SSR handling and DSP enablement.
Fix this by acquiring the ssr_mutex during enabling DSP and
sequence to list operations such that there is no race conditions.

Change-Id: I15c55bf96737e4ffd7e0faf571a1109ba6c38163
Signed-off-by: Bhalchandra Gajare <gajare@codeaurora.org>
Signed-off-by: Xiaoyu Ye <benyxy@codeaurora.org>