ANDROID: virt: gunyah: Move send_lock around req and reply

Gunyah resource manager has limited internal buffering to send messages
to VMs and it is possible to fill the buffer and cause RM to drop
replies. Prevent the "drop" scenario by serializing the entire
send/receive RPC flow.

Bug: 344815940
Change-Id: I65f2f6daf495eb24e1bc120a6a4d0b84c966e3cc
Signed-off-by: Elliot Berman <quic_eberman@quicinc.com>
(cherry picked from commit 7d911a14)