msm: pil-q6v5-mss: Set the force stop bit and wait for ack when necessary

The force stop bit can be used to indicate to the modem to dump its memory
and stop execution. The dumped memory can then be used for debugging
purposes.

This should be done under the following circumstances:

1. When the application processor panics, we need the modem image to stop
execution and dump its memory for future analysis. Setting the force stop
bit achieves this. But in this scenario use a timeout and do not wait for
the acknowledgement from the modem because all interrupts would be disabled
in the application processor.

2. When an SSR is being performed on the modem as part of a group of
subsystems where the SSR is not a direct result of the modem crashing but
because of any other subsystem in the group. In this case, dumping the
modem memory can help debug if there were any interdependencies between
the subsystems in the group which led to the SSR.

3. When an independent SSR is being performed where the modem doesn't
detect an error (and hence doesn't flush its buffer on its own) but a
client running on the application processor detects an error. The memory
dump then could lead to finding the cause of the error.

In cases 2 and 3, wait for the force stop acknowledgement from the modem
before proceeding further.

Change-Id: I816b53fb961adf93943893793e38254cb8bfcde1
Signed-off-by: Seemanta Dutta <seemanta@codeaurora.org>