Define only the CP15 register operations that are valid for the architecture.

Submitted by: Svatopluk Kraus <onwahe@gmail.com>,
              Michal Meloun <meloun@miracle.cz


git-svn-id: svn+ssh://svn.freebsd.org/base/head@276213 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f