sys: add MBM device ioctl() values

This is part of the upcoming USB umb(4) work. It implements the control
ioctl(4)s that MBM devices will need to implement.

Differential Revision: https://reviews.freebsd.org/D48167
Approved by: adrian, zlei
Sponsored by: FreeBSD Foundation
PR: kern/263783
Submitted by: Pierre Pronchery <khorben@defora.org>

(cherry picked from commit e5f3620a3e12c0febab7e4125da526c59a5a195b)