rangeset: add next() for iteration

[dougm]

Summary

Add a method rangeset_next to find the first range that starts at or after a given value. Use it to rewrite pmap_pkru_same to avoid walking a page at a time over pages in no range.

Test Plan

A kernel builds and boots.

[dougm]

Make similar changes for arm64.

[andrew]

sys/arm64/arm64/pmap.c

9296

Shouldn't we use va here?

[dougm]

Fix lazy editting observed by @andrew

sys/arm64/arm64/pmap.c

9296

Yep.

[dougm]

Typos abound. Squashed another.

[alc]

@kib Do you have any PKU test programs that could be run to check this?

[kib]

In D45511#1038472, @alc wrote:

@kib Do you have any PKU test programs that could be run to check this?

Specifically to check this patch, probably not. Existing PKRU tests were imported as tools/test/stress2/misc/pkru.sh and pkru2.sh.