drm/amd/display: Add function to create 4d19 fixed point

[Why]
Implemented for future use

Signed-off-by: Tyler DiBattista <tyler.dibattista@amd.com>
Reviewed-by: Eric Bernstein <Eric.Bernstein@amd.com>
Acked-by: Bhawanpreet Lakha <Bhawanpreet.Lakha@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>