drm/amd/display: Read DP tunneling support only for DPIA endpoints

drm/amd/display: Read DP tunneling support only for DPIA endpoints

Unconditionally reading DP tunneling support results in extraneous
errors messages on certain devices. Fix this by guarding the DPCD read
for DP tunneling support for USB4 DPIA endpoints.

Reviewed-by: Meenakshikumar Somasundaram <meenakshikumar.somasundaram@amd.com>
Signed-off-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Signed-off-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>