drm/amd/display: remove use_native_pstate_optimization

[Why]
In DML2 (not DML2.1), DCN35 and DCN351 have the
default value for use_native_pstate_optimization
set to true. The code path where this bit is
false is not used.

[How]
Remove the bit and the corresponding code path
when it is set to false.

Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Reviewed-by: Aric Cyr <aric.cyr@amd.com>
Signed-off-by: Yan Li <yan.li@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>