riscv: rework CPU identification [6/6]

[mhorne]

Summary

Detect and report the supported MMU for each CPU. This information is
not currently needed elsewhere in the kernel, but should be trivial to
export in the future.

[markj]

This information is not currently needed elsewhere in the kernel

The riscv kernel can run in SV48 mode if the user specifies a tunable requesting it. Presumably pmap_bootstrap() should be explicitly checking for that capability?

[mhorne]

In D39814#906688, @markj wrote:

This information is not currently needed elsewhere in the kernel

The riscv kernel can run in SV48 mode if the user specifies a tunable requesting it. Presumably pmap_bootstrap() should be explicitly checking for that capability?

I did look at that bit where you set up satp, and it recovers gracefully when SV48 is not supported so I didn't bother making this info public. But it would not hurt to do so.

[mhorne]

Export mmu_caps to the rest of the kernel and check it in pmap_bootstrap().

[mhorne]

Rebase.