Deprecate the 'devclass' argument from *DRIVER_MODULE() macros.

This argument is useless for the vast majority of drivers. For now,
use VA_ARGS wrapper macros so that that the *DRIVER_MODULE()
macros accept both the old version (with a devclass) and the new
version (which omits the argument and stores NULL in the
driver_module_data structure). This provides an API compatiblity
shim that can be merged to older stable branches.

Once all drivers relevant to 14.0 (both in and out of tree) have been
updated, the API compat shims can be dropped.

Reviewed by: imp
MFC after: 2 weeks
Differential Revision: https://reviews.freebsd.org/D34963

(cherry picked from commit 2a99dd30dfaac98fea79f084b3a13c45199e1348)
(cherry picked from commit 0fdf5bc531fbde4fa80a85614ba40230062ebde4)
(cherry picked from commit b7d4192598fed6581be627fc767f06a62195dfd5)