arm64: add page-to-pte convenience macros

[dougm]

Summary

Define macros to perform pte to vm_page and vm_page to pte conversions without composing two macros, and use the convenience macros wherever possible.

[dougm]

Combine two short lines into one.

[alc]

sys/arm64/arm64/pmap.c

540–541

A better place for these definitions is right before the definition of ATTR_SW_DBM.

[dougm]

Move macro definitions, as suggested.