dsp: q6afe: fix sleeping function called from invalid context

afe_callback indirectly calls q6core_send_uevent which might
sleep due to use of mutex. Move this send uevent function call
to work queue to prevent the issue.

Change-Id: I74ad151a9bae84860059d0a11042cda6475394c2
Signed-off-by: Xiaoyu Ye <benyxy@codeaurora.org>