soc: qcom: smp2p: Fix simultaneous access of global loopback data

Running SMP2P tests from multiple threads causes simultaneous access to
the global loopback data and resulting into unexpected behavior.

Protect the global loopback data by synchronizing the SMP2P tests.

CRs-Fixed: 2041374
Change-Id: Ifb0e7ce5198af27602881a9132afb353f1a4fc2f
Signed-off-by: Arun Kumar Neelakantam <aneela@codeaurora.org>