xilinx: drm: dp: Add the address only aux command

For start and stop of I2C transaction, the I2C command is sent without
any buffer. In this case, use the address only aux command, so that
the I2C transaction can be reset.

Signed-off-by: Hyun Kwon <hyun.kwon@xilinx.com>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>