[X/Y/Z][v2] ath10k: search SMBIOS for OEM board file extension

[Shrirang Bagul]

BugLink: https://bugs.launchpad.net/bugs/1666742

Patches for ath10k driver to read board variant from SMBIOS.

Patch for Zesty is a clean cherry-pick. Yakkety and Xenial are backports
only due to difference in context.

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.