Add 3 long options for getting information about mkimg itself:
--version	print the version of mkimg and also whether it's
		64- or 32-bit.
--formats	list the supported output formats separated by space.
--schemes	list the supported partitioning schemes separated by
		space.

Inspired by a patch from: gjb@

MFC after:	1 week
Relnotes:	yes
Remove an un-needed bit of pre-processor work - it all lives inside
#ifdef RSS.
cxgbe(4): implement if_get_counter.
* Split tcp_signature_compute() into 2 pieces:
 - tcp_get_sav() - SADB key lookup
 - tcp_signature_do_compute() - actual computation
* Fix TCP signature case for listening socket:
  do not assume EVERY connection coming to socket
  with TCP_SIGNATURE set to be md5 signed regardless
  of SADB key existance for particular address. This
  fixes the case for routing software having _some_
  BGP sessions secured by md5.
* Simplify TCP_SIGNATURE handling in tcp_input()

MFC after:	2 weeks
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.
Revert r272189, the committed version was an old version and breaks build.

Pointy hat to:	delphij
Add machine/sysreg.h to simplify accessing the system control coprocessor
registers and use it in the ARMv7 CPU functions.

The sysreg.h file has been checked by hand, however it may contain errors
with the comments on when a register was first introduced. The ARMv7 cpu
functions have been checked by compiling both the previous and this version
and comparing the md5 of the object files.

Submitted by:	Svatopluk Kraus <onwahe at gmail.com>
Submitted by:	Michal Meloun <meloun at miracle.cz>
Reviewed by:	ian, rpaulo
Differential Revision: https://reviews.freebsd.org/D795