drm/amd/display: Clean up warnings in amdgpu_dm _mst_types, _plane, _psr.c

Fix the following warnings reported by checkpatch:

WARNING: Missing a blank line after declarations
WARNING: Prefer 'unsigned int' to bare use of 'unsigned'

Cc: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Cc: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>