drm/amd/display: Remove always-false branches

[WHAT & HOW]
req128_c is always set to false and its branch is never taken.
Similarly, MacroTileSizeBytes is set to either 256 or 65535 and it is
never 4096 and it's branch is not taken.

Therefore, their branches are removed.

This fixes 3 DEADCODE issues reported by Coverity.

Acked-by: Alex Hung <alex.hung@amd.com>
Reviewed-by: Alvin Lee <alvin.lee2@amd.com>
Reviewed-by: Rodrigo Siqueira <rodrigo.siqueira@amd.com>
Signed-off-by: Alex Hung <alex.hung@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>