arm64: update the set of HWCAP definitions

This is in sync with what is defined for Linux 5.8. Note that all bits
in HWCAP are exhausted, and HWCAP2 has been added.

This also revealed an error in some of the existing definitions. We are
missing HWCAP_ASIMDHP, and as a result a portion of the HWCAP values are
shifted right by one bit. This will be fixed in an upcoming change, but
the values being added now are compatible with what Linux defines.

Reviewed by: emaste, markj, manu
MFC after: 1 week
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D26030