ath11k: add device-specific firmware for QCM6490 boards

ath11k: add device-specific firmware for QCM6490 boards

Most likely because of the TZ differences, on QCM6490 / QCS6490 boards
the WPSS DSP can not work with the existing firmware (provided for
SC7280 platforms). Add device-specific firmware for these boards.

The firmware comes in the MBN format rather than the typical MDT + Bnn
as the firmware file is being loaded through the remoteproc / DSP.

Compatibility links are added to follow the names in the existing DTs
(qcom/qcm6490-idp.dts and qcom/qcs6490-rb3gen2.dts).

Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>