drm/amd/display: Remove MPC rate control logic from DCN30 and above

[Why]
MPC flow rate control is not needed for DCN30 and above. Current logic
that uses it can result in underflow for certain edge cases (such as
DSC N422 + ODM combine + 422 left edge pixel).

[How]
Remove MPC flow rate control logic and programming for DCN30 and above.

Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Reviewed-by: Wenjing Liu <wenjing.liu@amd.com>
Acked-by: Tom Chung <chiahsuan.chung@amd.com>
Signed-off-by: George Shen <george.shen@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>