st-hal: fix session pause and lpi switch for concurrency

-for dedicated path, even when session is allowed, still need
 to check if session should be switched between lpi and non-lpi.
-for non-dedicated path, the global flag of session allow should
 be recorded when concurrency is not allowed.
-check global flag before switching LPI mode for handling screen
 state and battery charging.

Change-Id: Ifb1c606aa218a36e45ba3f3e071828f6fe06169d
1 file changed