Port to RISC-V Linux

[SEmmmer]

This is experimental and not guaranteed to work (it just compiles under QEMU)

My uname -a

Linux fedora-riscv 5.5.0-0.rc5.git0.1.1.riscv64.fc32.riscv64 #1 SMP Mon Jan 6 17:31:22 UTC 2020 riscv64 riscv64 riscv64 GNU/Linux

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[mtijanic]

Thank you for the interest and this PR! It is shaping up really well.

We do need to figure out internally how to handle additional architectures first, so expect some back and forth here and please have patience. But that shouldn't preclude the work to get the driver functional and we'll gladly help with that.

[X547]

I kind of managed to run this driver on HiFive Unmatched RISC-V machine and Haiku. I got display output, but also got some obscure problems that display start working only after connecting to another GPU port (and yet another on each boot). Interestingly problem is also observed on Linux Nouveau KMD.