video: exynos_dp: increase AUX channel voltage level

The value of AUX channel differential amplitude current is changed
from 8 mA to 16 mA, in order to increase AUX channel voltage level.
In this case, AUX channel voltage level can be changed from 400 mV
to 800 mV, when resistance between AUX TX and RX is 100 ohm.

According to DP spec, although the normative voltage level is 390 mV,
the informative voltage level is 430 mV. So, 800 mV can be helpful
to improve voltage margin of AUX channel.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Signed-off-by: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>