drm: tegra: remove redundant tegra2_tmds_config entry

The 720p and 1080p entries are completely redundant, as we are matching
the table entries against <=pclk.
Also generalize the comment, as we are using those table entries even
when driving other modes than the standard TV ones.

Signed-off-by: Lucas Stach <dev@lynxeye.de>
Signed-off-by: Dave Airlie <airlied@redhat.com>