drm/amd/display: fix i2c wtire mot incorrect issue

[Why]
I2C write command always send mot = true will cause sink state incorrect.

[How]
1. Remove default i2c write mot = true.
2. Deciding mot flag by is_end_of_payload flag.

Signed-off-by: Lewis Huang <Lewis.Huang@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>