msm: ADSPRPC: close glink channel in restart notification

Closed glink channel in subsystem restart notification only,
instead of subsystem restart and glink remote disconnected
notifications for avoiding race conditions.
Reverted the use mutex at channel context level to global apps
context.

Change-Id: I4ac6b87aa4bf9e091277b803e7b7fe1a5274f419
Acked-by: Viswanatham Paduchuri <vpaduchu@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>