[Xorg-driver-geode] Mode validation issue in geode driver

[Huang, FrankR]

According to my debug on X server and geode driver, I am more clear
about this part code(src/lx_output.c lx_output_mode_valid()).
In the X server function xf86ProbeOutputModes(), there are three types
of modes. They are conf_modes, output_modes, default_modes. 
1)The Modeline in xorg.conf is recorded in conf_modes(such as 1440x900),
then in output->probed_modes.
2)The Other modes are detected from monitor and recorded in
output_modes(such as 1024x768, 800x600).
3)The default_modes is NULL. 
All these modes are added to output->probed_modes with function
xf86ModesAdd(). Then these modes will be validated by driver's output
function mode_valid. For geode, it is lx_output_mode_valid().
For Intel, it is:
http://cgit.freedesktop.org/xorg/driver/xf86-video-intel/tree/src/intel_
display.c intel_output_mode_valid()
For ATI, it is:
http://cgit.freedesktop.org/xorg/driver/xf86-video-ati/tree/src/radeon_o
utput.c  radeon_mode_valid()