ath10k: support bus and device specific API 1 BDF selection

Some ath10k IPQ40xx devices like the MikroTik hAP ac2 and ac3 require the
BDF-s to be extracted from the device storage instead of shipping packaged
API 2 BDF-s.

This is required as MikroTik has started shipping boards that require BDF-s
to be updated, as otherwise their WLAN performance really suffers.
This is however impossible as the devices that require this are release
under the same revision and its not possible to differentiate them from
devices using the older BDF-s.

In OpenWrt we are extracting the calibration data during runtime and we are
able to extract the BDF-s in the same manner, however we cannot package the
BDF-s to API 2 format on the fly and can only use API 1 to provide BDF-s on
the fly.
This is an issue as the ath10k driver explicitly looks only for the
board.bin file and not for something like board-bus-device.bin like it does
for pre-cal data.
Due to this we have no way of providing correct BDF-s on the fly, so lets
extend the ath10k driver to first look for BDF-s in the
board-bus-device.bin format, for example: board-ahb-a800000.wifi.bin
If that fails, look for the default board file name as defined previously.

Signed-off-by: Robert Marko <robimarko@gmail.com>
Signed-off-by: Kalle Valo <quic_kvalo@quicinc.com>
Link: https://lore.kernel.org/r/20211009221711.2315352-1-robimarko@gmail.com