disp: msm: dsi: Fix DMA window scheduling programming

In DMA start window scheduling, TRIG_CTRL.COMMAND_MODE_DMA_TRIGGER_SEL
is programmed to SW + DMA start window trigger. But if DMS switch
comes after command is scheduled, COMMAND_MODE_DMA_TRIGGER_SEL gets
reprogrammed to SW trigger leading to command transfer failure.

Program the COMMAND_MODE_DMA_TRIGGER_SEL only from the CMD DMA Tx path.

Change-Id: I01062497bb70aa5fdcb25be3715c7cbc4c68b681
Signed-off-by: Ritesh Kumar <quic_riteshk@quicinc.com>
Signed-off-by: Rajeev Nandan <quic_rajeevny@quicinc.com>