We frequently need to check if a vnode refers to either a character or
block special, so we might as well have a macro for it.
We somewhat less frequently need to perform similar checks on things
that aren't vnodes (usually a struct vattr *), so add VATTR_ISDEV()
and a generic VTYPE_ISDEV() as well.
Sponsored by: Klara, Inc.
Sponsored by: NetApp, Inc.
Reviewed by: kib
Differential Revision: https://reviews.freebsd.org/D51947