Add kernel support for the TP-LINK MR3020 Atheros MIPS 24k router.

AR9331 based system.

Phabric:	https://reviews.freebsd.org/D780
Reviewed by:	adrian
Switch primes(6) from using unsigned long to using uint64_t.  This fixes
'limited range of type' warnings about comparisons on 32-bit systems, and
allows 32-bit systems to compute the full range of primes.