drm/amd/display: Adding braces to prepare for future changes to behavior of if block

[Why & How]
For certain features, there will be more implementations needed in the if-block.
Braces are added as part of the preparation.

Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Leo Chen <sancchen@amd.com>
Reviewed-by: Charlene Liu <Charlene.Liu@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>