Move mips and arm to 1000Hz by default.

armv6 and armv7 systems already were 1000Hz. The other armv5 were a
mix of 100 and 1000. This changes them to 1000. Should there be
issues, we can add options HZ=100 to the systems that have bad
performance at the drop of a hat.

mips is a lot more complicated. But most of the systems are already
1000HZ. The hardware exceptions are all fast enough to run at
1000Hz. MALTA is our primary emulator, and history has shown emulators
tend to like 100Hz better, so run those systems at 100Hz. As with arm,
any system that shows a huge performance regression can reverted to
100Hz easily.

This was going to be committed well in advance of the 13 branch, but
it was delayed and forgotten til now.

Discussed on: #bsdmips ages ago
Sponsored by: Netflix