bsdinstall: riscv platform tweaks

[mhorne]

Summary

Make the installer more useful by allowing it to create a bootable
installation. RISC-V boots with UEFI only.

• Enable ZFS root install option
• Enable creation of bootable ESP

Test Plan

Install and boot with a ZFS root filesystem.
Install and boot with a UFS root filesystem.

[mhorne]

Note that partedit_riscv.c is practically identical to partedit_arm64.c. We could merge the two, I'm just not sure what it ought to be called.

[gjb]

Note, I only looked closely at the shell-based changes, considering partedit_riscv.c is identical to its amd64 counterpart.

[emaste]

In D28180#629764, @mhorne wrote:

Note that partedit_riscv.c is practically identical to partedit_arm64.c. We could merge the two, I'm just not sure what it ought to be called.

partedit_gpt_uefi.c maybe?

[mhorne]

Rename and merge the partedit_*.c files.

[mhorne]

In D28180#629992, @emaste wrote:

In D28180#629764, @mhorne wrote:

Note that partedit_riscv.c is practically identical to partedit_arm64.c. We could merge the two, I'm just not sure what it ought to be called.

partedit_gpt_uefi.c maybe?

Thanks. I dropped the gpt only because there is nothing that precludes MBR from being allowed as well, other than we've chosen not to.

[mhorne]

Fix arm64 $MACHINE check.

[mhorne]

Now tested on arm64 as well. If all seems good, I will commit and MFC to stable/13 before the branch.