qseecom: Fix issues on key management scheme

The mechanism to update how a user is tied to an existing key is
added. And the app_access_lock mutex is removed in key management
APIs, as there is no need to lock app access while processing a
key related request.

Change-Id: Ib017f55a7af48ed01001e69022fd9732cedef8cc
Signed-off-by: Zhen Kong <zkong@codeaurora.org>