Setup native RISC-V builder
Context
RISC-V build is available for Freedesktop SDK, but there is no native runner, so CI for RISC-V is not always run.
Description
We try to set up a reasonably powerful runner for RISC-V, so CI for RISC-V won't take long.
A candidate machine model is Milk-V Pioneer.
We should test builds on each candidate machine model, to check whether it is fast enough.
Then we figure out how to make the builder accessible from Gitlab, whether to host the machine at OSU or elsewhere.
Acceptance Criteria
RISC-V CI runs on a native builder.