hdmitx: hdmitx bringup for tm2 [3/3]

hdmitx: hdmitx bringup for tm2 [3/3]

PD#SWPL-5617

Problem:
hdmitx bringup for tm2

Solution:
echo null > /sys/class/display/mode
echo 1080p60hz > /sys/class/display/mode

test method:
echo bist1920 > /sys/class/amhdmitx/amhdmitx0/debug
echo bistoff > /sys/class/amhdmitx/amhdmitx0/debug

Verify:
tm2 ptm

Change-Id: I4c69ec1e1e26c1ae7fde0fca5cd8b98c13e609f2
Signed-off-by: Yi Zhou <yi.zhou@amlogic.com>
Signed-off-by: Zongdong Jiao <zongdong.jiao@amlogic.com>