arm64: export a few more HWCAPs

These were missed in the previous pass. The extensions (partially)
supported by this change are:

• ARMv8.2-FHM, Floating-point multiplication variant
• ARMv8.4-LSE, Large System Extensions
• ARMv8.4-DIT, Data Independent Timing instructions

Reviewed by: andrew, markj
Sponsored by: The FreeBSD Foundation
Differential Revision: https://reviews.freebsd.org/D26707