drm/radeon/kms: refine TMDS dual link checks

HDMI 1.3 defines single link clocks up to 340 Mhz.
Refine the current dual link checks to only enable
dual link for DVI > 165 Mhz or HDMI > 340 Mhz if the
hw supports HDMI 1.3 (DCE3+).

Fixes:
https://bugs.freedesktop.org/show_bug.cgi?id=44755

Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>