Add the mfi(4) ioctl support to mrsas(4)

The hardware supported by mfi(4) and mrsas(4) use the same dcmd's.
mfiutil(8) in theory could run on controlled attached to mrsas(4).
It can't since mrsas(4) doesn't have support for the FreeBSD mfi(4)
ioctl. Porting the ioctl from mfi(4) to mrsas(4) would be the first
step in making mrsasutil(8) which is an additional name for mfiutil(8)
but opens /dev/mrsasX instead of /dev/mfiX

PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=265794
Reviewed by: jhb
Differential revision: https://reviews.freebsd.org/D36342
Tested by: Dan Mahoney <freebsd@gushi.org>