rpmsg: glink: Transition intent request signaling to wait queue

Transition the intent request acknowledgement to use a wait queue so
that it's possible, in the next commit, to extend the wait to also wait
for an incoming intent.

Signed-off-by: Bjorn Andersson <quic_bjorande@quicinc.com>
Reviewed-by: Chris Lew <quic_clew@quicinc.com>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230327144617.3134175-2-quic_bjorande@quicinc.com