x11/nvidia-driver: Split kmod into x11/nvidia-kmod

Split out kmod part of x11/nvidia-driver into x11/nvidia-kmod,
including slave ports, to allow FreeBSD-kmods repo builders building
nvidia-related kmod ports.

In this update,

• split out *.ko from x11/nvidia-driver[-304|-340|-390|470|-devel] into corresponding x11/nvidia-kmod[-304|-340|-390|470|-devel],

• switch dependency of graphics/nvidia-drm-*-kmod upon x11/nvidia-driver[-devel] to newly introduced x11/nvidia-kmod[-devel],

• make x11/nvidia-driver[-304|-340|-390|470|-devel] depend upon newly introduced x11/nvidia-kmod[-304|-340|-390|470|-devel],

• bump consumers directly depending upon x11/nvidia-driver* as of dependency switches,

• and hook x11/nvidia-kmod[-304|-340|-390|470|-devel] to build.

Note that upgrading x11/nvidia-driver* from monolithic version
requires deinstallation of x11/nvidia-driver* before starting,
as both previous version of x11/nvidia-driver* and newly introduced
x11/nvidia-kmod* installs *.ko into same place.

PR: 288314
Approved by: bapt (kmod repo)
Differential Revision: https://reviews.freebsd.org/D52178