soc: qcom: glink_smd_xprt: Serialized open ack notify and signal event

SMD channel can get into OPENED state before even the G-Link channel
gets into OPENED/CONNECTED state. This can cause the SMD channel events
to get dropped.

Synchronize handling the SMD_OPEN_EVENT & subsequent events in an SMD
channel with the G-Link channel open operation.

CRs-Fixed: 997404
Change-Id: I4c44011b7fa3b59cbe70a125735e04a076c4d3ca
Signed-off-by: Dhoat Harpal <hdhoat@codeaurora.org>