Remove unneeded masks from the arm64 KASAN shadow

When mapping the arm64 KASAN shadow map we use Ln_TABLE_MASK to align
physical addresses, however these should already be aligned either
by rounding to a greater alignment, or the VM subsystem is giving us
a correctly aligned page.

Remove these extra alignment masks.

Reviewed by: kevans
Sponsored by: Arm Ltd
Differential Revision: https://reviews.freebsd.org/D39752