drm/amd/display: Add usb4_bw_alloc_support flag

drm/amd/display: Add usb4_bw_alloc_support flag

[Why]
dc should have a flag for DM to enable usb4_bw_alloc in dptx

[How]
- Add usb4_bw_alloc_support flag in dc_config

Reviewed-by: Wayne Lin <wayne.lin@amd.com>
Reviewed-by: Meenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>
Acked-by: Roman Li <roman.li@amd.com>
Signed-off-by: Peichen Huang <peichen.huang@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>