ath10k: search SMBIOS for OEM board file extension

Board Data File (BDF) is loaded upon driver boot-up procedure. The right
board data file is identified, among others, by device and sybsystem ids.

The problem, however, can occur when the (default) board data file cannot
fulfill with the vendor requirements and it is necessary to use a different
board data file.

To solve the issue QCA uses SMBIOS type 0xF8 to store Board Data File Name
Extension to specify the extension/variant name. The driver will take the
extension suffix into consideration and will load the right (non-default)
board data file if necessary.

If it is unnecessary to use extension board data file, please leave the
SMBIOS field blank and default configuration will be used.

Example:
If a default board data file for a specific board is identified by a string
      "bus=pci,vendor=168c,device=003e,subsystem-vendor=1028,
       subsystem-device=0310"
then the OEM specific data file, if used, could be identified by variant
suffix:
      "bus=pci,vendor=168c,device=003e,subsystem-vendor=1028,
       subsystem-device=0310,variant=DE_1AB"

If board data file name extension is set but board-2.bin does not contain
board data file for the variant, the driver will fallback to the default
board data file not to break backward compatibility.

This was first applied in commit f2593cb1 ("ath10k: Search SMBIOS for OEM
board file extension") but later reverted in commit 005c3490 ("Revert
"ath10k: Search SMBIOS for OEM board file extension"". This patch is now
otherwise the same as commit f2593cb1 except the regression fixed.

Signed-off-by: Waldemar Rymarkiewicz <ext.waldemar.rymarkiewicz@tieto.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>