Galileo screen stays off after undocking when resolution >720p

[Sterophonick]

When undocking a Galileo unit in game mode, the screen tends to stay turned off and is not fixed until a session restart. This can be worked around if the resolution is forced to 720p on the external screen.

Matching SteamOS issue: https://github.com/ValveSoftware/SteamOS/issues/1504