Build on aarch64

[valpackett]

This PR adds some basic portability and makes radeon and amdgpu build on aarch64. Does not include openfirmware stuff (damn that's a lot of API surface), only works with the existing PCIe support.

radeon loads and says this:

[drm] radeon kernel modesetting enabled.

amdgpu doesn't load (this is a soft FPU function, I guess we need a flag other than -mhard-float??):

link_elf: symbol __eqdf2 undefined

Whether it actually works is not tested… porting rkpcie would be the first requirement on my hardware (RK3399), and then there's the issue of whether u-boot configures pci correctly. Marvell Armada 8k (MACCHIATObin) is at least known to work with GPUs on Linux, but we don't yet have pcie on that either. I guess if someone has physical access to a ThunderX box, they can test it :D Jetson TX1 might have PCIe working too?

[iotamudelta]

@johalun any opinions on this?

If it looks good to you, I'm happy to test it for the port.

[johalun]

No makefiles in the drivers/ subfolders are used so no need changing them. We have to remember to pull this in to 4.17 later also.

[johalun]

@myfreeweb Can you revert the changes to makefiles in drivers/ so we don't get merge fail on those later?

[evadot]

I don't see the point of merging something that isn't tested.
Loading module is one thing, using them is another thing (trust me on this).

[mattmacy]

Is there anyone with an arm64 with a radeon or amdgpu graphics card to test? Otherwise I'm inclined to agree with @evadot I didn't push my power changes until I had confirmed that the driver at least attached.

[mattmacy]

@myfreeweb Can we close this? The POWER support changes should make this easier to add in the future if someone has appropriate hardware.

[valpackett]

Yes, I'll redo this on top of the POWER changes when I get hardware to test on. (btw, did you find anything from this PR useful for the POWER changes?)