drm/amd/display: Do not grant POST_LT_ADJ when TPS4 is used

[Description]

The spec does not allow POST_LT_ADJ_GRANTED to be set when TPS4 is used.

Signed-off-by: abdoulaye berthe <abdoulaye.berthe@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>