drm/amd/display: rename bandwidth_calcs.c to dce_calcs.c (v2)

v2: agd: squash in the Makefile change as well.

Signed-off-by: Dmytro Laktyushkin <Dmytro.Laktyushkin@amd.com>
Acked-by: Harry Wentland <Harry.Wentland@amd.com>
Reviewed-by: Eagle Yeh <eagle.yeh@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>