qseecom: Change mutex operation for qseecom_unload_app

qseecom_unload_app is protected between global mutex lock/unlock.
And it will wait until all other ioctl functions related to the
same process are finished, then unload app.
When reentrancy is enabled and mutex is hold during sleep, another
cmd for the same app that tries to grab mutex may cause deadlock.
So we make change to unlock mutex before sleep and re-locked it
again after wake up.

Change-Id: I60eca546ba82e7261296202f941a416be5f898df
Signed-off-by: Zhen Kong <zkong@codeaurora.org>