cnss2: Avoid race condition between time sync and system suspend

Add mutex to protect time sync operation and PCIe bus suspend from
system suspend to avoid race condition between msm_pcie_pm_suspend
and msm_pcie_prevent_l1/allow_l1.

Change-Id: I8ff0f258e8928b97deeada134982ee2cbe93ae9a
Signed-off-by: Yue Ma <yuem@codeaurora.org>