drm/amd/include: Add USB_C_TYPE to atom_encoder_cap_defs

This is needed by DC to support EDID emulation on USB-C ports.

CC: Samson Tam <Samson.Tam@amd.com>
CC: Harry Wentland <harry.wentland@amd.com>
CC: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Leo Li <sunpeng.li@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>