Add mrsasutil(8) as alias to mfiutil(8)

mfiutil(8) in theory can work on devices attached to mrsas(4) but
mrsas(4) is missing the FreeBSD mfi(4) ioctl support. Once that
support is added to mrsas(4) then mrsasutil(8) can manage mrsas(4)
attached devices. So this commit depends on that. When mrsasutil(8)
is run it automatically opens /dev/mrsas0 instead of /dev/mfi0.
Add -D <device> and -t <type> flag to optionally specify mrsas or mfi to
work with the existing -u <unit>. Device is the device node with or
without /dev/

PR: https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=265794
Differential Revision: https://reviews.freebsd.org/D36343
Tested by: Dan Mahoney <freebsd@gushi.org>
Reviewed by: jhb