Fix bracketing in the arm64 minidump code

When building with gcc10 it suggests the parentheses are wrong. Set them
to be the calculated physical address or'd with page table attributes.

Reviewed by: mhorne, imp
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D33099

(cherry picked from commit 3ff041945054e692672f506a2448d1200133032d)