cnss2: Expose PCIe window register lock related APIs

The register window needs to be configed properly before accessing
any larger than 4K range PCIe registers. Expose the lock to WLAN
driver to avoid race condition when both drivers try to config it.

Change-Id: I94ccd963d4fd0a9715330d2e5733346ccd993ae1
Signed-off-by: Yue Ma <yuem@codeaurora.org>