msm: cpp: Synchronize writing payload to cpp hardware

When the system is slow, interrupt is received from cpp hardware
just after driver times out. Tasklet processes the interrupt and
sends buffer done. A new frame is send from userspace and is
written to the hardware at the same time firmware is written.
This causes CPP hardware to be in bad state and poll failures are
observed. This can cause stability crashes. The fix is to
synchronize writing payload from user thread and firmware from
work queue.

CRs-Fixed: 910559 919550
Change-Id: I75594b5202f0bed39840b36064f4e21b03e83355
Signed-off-by: Krishnankutty Kolathappilly <kkolatha@codeaurora.org>