geom: Add HiFive boot partitions

[emaste]

Summary

As documented in the HiFive Unmatched Software Reference Manual.

e.g. ubuntu-21.04-preinstalled-server-riscv64+unmatched.img:

=>     34  7339965  md0  GPT  (3.5G)
       34     2048   13  hifive-fsbl  (1.0M)
     2082     8192   14  hifive-bbl  (4.0M)
    10274   217088   15  efi  (106M)
   227362     8192   12  linux-data  (4.0M)
   235554  7104445    1  linux-data  (3.4G)

[imp]

ARM should have done this for their 'hidden' boot partitions years ago. Glad to see this being done in riscv land.

One question, though, is that are these hifive specific, or something more general that we've only seen on hifive so far...

[mhorne]

In D34010#768950, @imp wrote:

ARM should have done this for their 'hidden' boot partitions years ago. Glad to see this being done in riscv land.

One question, though, is that are these hifive specific, or something more general that we've only seen on hifive so far...

So far they are hifive-specific. Hopefully this scheme will be adopted more widely, but if it ends up that different vendors use different IDs or layouts it will just make the whole situation messier, at least from the POV of providing release images.