drm/amd/display: Change the order of setting DP_IS_USB_C flag

[Why]
enc10->base.features.flags.bits.DP_IS_USB_C will be overwritten if we set it
before initializing enc10->base.features

[How]
Determine DP_IS_USB_C after enc10->base.features is initialized. Besides,
bp_cap_info.DP_IS_USB_C will never be set in get_connector_speed_cap_info().
Remove the redudant code.

Reviewed-by: Roman Li <roman.li@amd.com>
Acked-by: Zaeem Mohamed <zaeem.mohamed@amd.com>
Signed-off-by: Wayne Lin <wayne.lin@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>