arm64: dts: qcom: enable dual ("bonded") DSI mode for DB845c

Now as both lt9611 and drm/msm drivers were updated to handle the 4k
modes over DSI, enable "bonded" DSI mode on DB845c. This way the board
utilizes both DSI links and thus can support 4k on the HDMI output.

Cc: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Reviewed-by: Konrad Dybcio <konrad.dybcio@linaro.org>
Signed-off-by: Bjorn Andersson <andersson@kernel.org>
Link: https://lore.kernel.org/r/20230504160430.4014206-1-dmitry.baryshkov@linaro.org