drm/radeon/kms: add initial connector properties

This adds:
coherent mode: TMDS coherent mode for atom cards.
scaling mode: LVDS scaler mode
load detect: DAC load detection, DVI-I, VGA, TV
tmds pll: legacy TMDS pll selection
tv standard: TV standard selection.

for later: other TV ones? dvi subconnector selection using std prop

[contains fixes pointed out on dri-devel for atom bios mixups
 by Michel]

Signed-off-by: Dave Airlie <airlied@redhat.com>