drm/amd/display: Do not set optimized_require to false after plane disable

[WHY]
The optimized_require flag is needed to set watermarks and clocks lower
in certain conditions. This flag is set to true and then set to false
while programming front end in dcn20.

[HOW]
Do not set the flag to false while disabling plane.

Signed-off-by: Sung Lee <sung.lee@amd.com>
Reviewed-by: Tony Cheng <Tony.Cheng@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>