On Ivy Bridge platform, when 3 display outputs are used, they can be used as
long as both displays connected to the second and third output share the same
resolution and refresh rate.

This tool allows to list possible combinations of outputs to be used for pipeB
and pipeC.

So the following scenarios would work:
- Just one output:
  - use xrandr as usual. Any resolution on any output should work.
- Two outputs
  - use xrandr as usual. Any resolution on any 2 outputs should work.
- Three outputs
  - for the first output (VGA, LVDS or eDP), use xrandr as usual. Any
    resolution should work.
  - for the 2nd and 3rd outputs, use one of the valid outputs which this tool
    can print out for you.

Example:

# xrandr
Screen 0: minimum 320 x 200, current 1600 x 900, maximum 8192 x 8192
LVDS1 connected 1600x900+0+0 (normal left inverted right x axis y axis) 309mm x 174mm
   1600x900       60.0*+   40.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
VGA1 disconnected (normal left inverted right x axis y axis)
HDMI1 connected (normal left inverted right x axis y axis) 0mm x 0mm
   1600x900       60.0*+   40.0  
   1024x768       60.0  
   800x600        60.3     56.2  
   640x480        59.9  
DP1 connected (normal left inverted right x axis y axis) 0mm x 0mm
   1600x900       60.0*+   40.0  
   800x600        60.3     56.2  
HDMI2 disconnected (normal left inverted right x axis y axis)
HDMI3 disconnected (normal left inverted right x axis y axis)
DP2 disconnected (normal left inverted right x axis y axis)
DP3 disconnected (normal left inverted right x axis y axis)

# ./xrandr.py
Valid modes for 3 display outputs:
--output DP1 --mode 1600x900 --rate 60.0 --output HDMI1 --mode 1600x900 --rate 60.0
--output DP1 --mode 1600x900 --rate 40.0 --output HDMI1 --mode 1600x900 --rate 40.0
--output DP1 --mode 800x600 --rate 60.3 --output HDMI1 --mode 800x600 --rate 60.3
--output DP1 --mode 800x600 --rate 56.2 --output HDMI1 --mode 800x600 --rate 56.2
--output HDMI1 --mode 1600x900 --rate 60.0 --output DP1 --mode 1600x900 --rate 60.0
--output HDMI1 --mode 1600x900 --rate 40.0 --output DP1 --mode 1600x900 --rate 40.0
--output HDMI1 --mode 800x600 --rate 60.3 --output DP1 --mode 800x600 --rate 60.3
--output HDMI1 --mode 800x600 --rate 56.2 --output DP1 --mode 800x600 --rate 56.2