drm/amd/display: Move mclk calculation function to DML

The function responsible for calculating the MCLK switching has FPU
operations. This commit moves it to the dcn30_fpu file.

Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>