drm/amd/display: Remove unnecessary eDP power down

[why]
When first time of link training is fail,
eDP would be powered down and
would not be powered up for next retry link training.
It causes that all of retry link linking would be fail.

[how]
We has extracted both power up and down sequence from
enable/disable link output function before DCN32.
We remov eDP power down in dcn32_disable_link_output().

Reviewed-by: Charlene Liu <charlene.liu@amd.com>
Signed-off-by: Yiling Chen <yi-ling.chen2@amd.com>
Signed-off-by: Tom Chung <chiahsuan.chung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>