soc: qcom: Replace SPCOM channel owner pid with tgid

SPU HAL server uses multiple RPC threads to handle HAL client requests.
pid is not shared between the threads which prevents releasing SPCOM
channels properly. tgid, the group ID which is shared between the
threads is used instead.

Change-Id: I7b119b386868364f3c476d1f6dfdf915aac8c306
Signed-off-by: Liron Daniel <lirond@codeaurora.org>