hdmitx: parse colorattribute from uboot [2/2]

hdmitx: parse colorattribute from uboot [2/2]

PD#SWPL-2181

Problem:
For some Rx, if the Tx cold boots up, the HPD can't be got in uboot.
That is to say, the output mode is CVBS in uboot, even HDMI cable is
connected. And during kernel boots up, it will reset to hdmi mode.
During the Android boots up, it will set to hdmi mode again. Twice
hdmi mode setting may cause TV flicks.

Solution:
Add parsing colorattribute from uboot and assign $attr to prevent
the second Android mode setting.

Verify:
S905X/P212

Change-Id: I665227bc3e8481acb40c34dde2f5cb3c633c64a2
Signed-off-by: Zongdong Jiao <zongdong.jiao@amlogic.com>