cnss: Unregister CNSS driver as PCIe device driver when PCIe link Fails

L2Cache errors are observed when PCIe framework tries to access
WLAN PCIe Config Space when PCIe link retraining fails.

PCIe framework is not aware of the  PCIe link retraining failure,
and hence PCIe framework tries to read the config space of WLAN.

Unregister CNSS driver to inform PCIe framework that WLAN
is not a PCIe device when PCIe link retraining fails.

Fix avoids L2 errors in situations when CLD driver register with CNSS.
If the PCIe link training/phy initialization fails during resume, we will
still face this issue. The best place would be to fix this is in the root
complex driver by disallowing the read/write of endpoint's config space.

Change-Id: I7685f597f77eb3d5cb6d1ba795ab19852c0e3542
CRs-fixed: 605797
Signed-off-by: Komal Seelam <kseelam@codeaurora.org>