Fix pmap_page_is_mapped() for arm64 and riscv.

[markj]

Summary

To be correct, this function needs to look at 2MB mappings as well. I
just copied the implementation from amd64.

[alc]

sys/arm64/include/pmap.h

170–171 ↗

(On Diff #62653)

You need to replace this by the function declaration from amd64:

boolean_t pmap_page_is_mapped(vm_page_t m);

[markj]

Add missing prototypes.

[alc]

Here is a take-it-or-leave comment: Consider conversion from "boolean_t" to "bool".