arm64/disassem.c: Add shifted register instruction definitions

Add disassembly support for the following shifted register instructions:

• adds
• subs
• sub
• neg
• negs
• cmp
• cmn

The 'Mandatory Tokens' checks are relaxed to allow for the alias
instructions (e.g. cmp) which hard-code one or more registers as xzr.

Reviewed by: mhorne
MFC after: 1 week
Differential Revision: https://reviews.freebsd.org/D40006