odroid/xu: use mainline kernel

[paralin]

Try using the mainline kernel on the Odroid XU4.

Tested on Odroid XU4 and appears to work correctly.

cc @danyer

[paralin]

This appears to work fine. However, there's a long list of commits on the odroid branch related to xu4 that we would drop:

I don't know if any of this is relevant, however, a few things stand out:

• The "not load RGB709 to YUV709 coefficient" fixes the screen being green on some displays
• Marking mmc0 as non-removable in the device tree fixed some bugs at one point
• Adding information about the xu4 improves the device name (now it's just Flattened Device Tree)
• Add i2c-1 and i2c-5 nodes is necessary for some users to use those i2c nodes.
• Is the regulator stuff related to ethernet power reset & proper shutdown still needed?
• Everything else I'm not familiar with & probably can be dropped.

Running the mainline kernel:

[paralin]

The main question @danyer is if this fixes your USB issue. If so, we can start to figure out which commits on the tobetter branch break it, and get rid of those. I still think keeping these XU4 patches would be the better option, and continuing to use the tobetter branch for all odroids would be better than using mainline for just 1 of the boards.

[paralin]

While this works on mainline I will close for now since there's no inherent advantage to using this over the skiffos tobetter branch. That branch has some xu4-related patches that I think are still relevant today.