Disable alignment faults on armv6, adjust various alignment-related macros
to match the new state of affairs. The hardware we support has always been
able to do unaligned accesses, we've just never enabled it until now.

This brings FreeBSD into line with all the other major OSes, and should help
with the growing volume of 3rd-party software that assumes unaligned access
will just work on armv6 and armv7.