cnss: FR: Secure Firmware Download using sha256 hash

Driver has to compute the SHA-256 hash for each FW bin.
Driver stores sha256 hash of each bin in global static variable.
Download FW bin if the computed hash matches with stored hash of
respective FW bin else bail out.
If Stored Hash entries are NULL, download fw in non-secure mode.
Host Driver will be secured by OEM.

CRs-Fixed: 707238
Change-Id: I553e7f905e8479357a328eadb8df9a3bd77b08a7
Signed-off-by: Komal Kumar <kseelam@codeaurora.org>