cnss: Add support for multiple revisions of CNSS FW

Detect the chip revision by reading REVISION ID in the PCI configuration
space, and setup the appropriate FW image files. WLAN driver will query
the CNSS driver for the FW files to be loaded.

Change-Id: Ib67fec52460cff1242b48959710b3163ef6c9b6a
Signed-off-by: Sameer Thalappil <sameert@codeaurora.org>