cnss2: Unregister host driver during PCI remove

CNSS2 registers as both platform and PCI driver. PCI
device can be removed via sysfs exposed by kernel during
PCI device creation. When PCI device gets removed, CNSS
PCI remove ops gets called. In cnss_pci_remove, unregister
host driver and shutdown WLAN chip to cleanly remove PCI
device.

Change-Id: Ia60e8b69bda2b3bdd5990cb83f47c082d6667283
Signed-off-by: Naman Padhiar <quic_npadhiar@quicinc.com>