Firmware should read EDID of output devices and warn about incompatibilities

[mithro]

So, we tested two resolution modes with Carl's monitor. 800x600 and 1024x768.

Setting video mode to 800x600 @56Hz
Setting video mode to 1024x768 @60Hz

Neither of these resolutions are supported by the EDID dump that Carl provided.

The firmware should warn if;

• A monitor is connected which doesn't support the resolution the system is set to.
• A resolution is set to a mode the connected monitors don't support.

This is related to #35 and possibly related to #18.

[enjoy-digital]

The sequence should be:

• Detect Hotplug Generate a message on the UART when hotplug level changes #33
• Dump EDID Dump EDID from connected monitor #35
• This issue Firmware should read EDID of output devices and warn about incompatibilities #37

[mithro]

@fallen