qseecom: update cumulative_mode and timer properly

qseecom.cumulative_mode is used to track the cummulative bus request
mode from all concurrent running clients. It is registered before
send_cmd operation, but is not un-registered after it is complete.
This may cause the bus bandwidth is restored to a wrong mode after
resuming from sleep. Thus, we make change to update it accordingly.
qseecom.current_mode is also updated in suspend/resume function to
ensure timer can scale down bus bw after resume when cumulative_mode
is non-zero. Besides, timer operation is optimized in case there are
multiple unserialized concurrent users of the same timer.

Change-Id: I06043d2b88a47e24da03460fe1ae26a94cb6a608
Signed-off-by: Zhen Kong <zkong@codeaurora.org>