dt: bindings: add new dt entry for ath11k calibration variant

dt: bindings: add new dt entry for ath11k calibration variant

The bus + qmi-chip-id + qmi-board-id is not enough to identify the correct
board data file on IPQ6018 based devices. Multiple different boards share
the same values. Only the original reference designs can currently be
identified and loaded from the board-2.bin. But these will not result in
the correct calibration data when combined with the pre-calibration data
from the device.

An additional "variant" information has to be provided to select the
correct board data for a design which was modified by an ODM. This follows
the same approach as ath10k.

Signed-off-by: Sven Eckelmann <sven@narfation.org>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20201015131501.1939685-1-sven@narfation.org