drm/amd/display/dc: Make dce110_validate_bandwidth static (v2)

Not used outside of the dce110_resource.c.

v2: make a bunch of other functions static as well.

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>