kbuild: Modify default INSTALL_MOD_DIR from extra to updates

kbuild: Modify default INSTALL_MOD_DIR from extra to updates

The default INSTALL_MOD_DIR of using the /lib/modules/$(uname -r)/extra
directory for external modules assumes distributions will have something
like  /etc/depmod.d/dist.conf with:

search updates extra built-in

However, only some Red Hat releases have and use the "extra" stuff for
years now. Meanwhile, the depmod.c tool in kmod has *forever* used
the "updates" directory as part of the search path by default *if*
your distribution does not have any depmod.d configuration.

If you compile and install an external module today, even upstream
kernel mock drivers (tools/testing/cxl) the modules_install target
will pick up the new drivers but will not allow override of drivers
from updates to override built-in ones.

Since module-init-tools was deprecated over 11 years ago and now kmod
has since its inception used the "updates" directory as part of its
default search path to allow overrides, and since the "extra" stuff
was in practice only used by Red Hat stuff, use the more distro
agnostic override path "updates" to allow external modules to
also override proper production kernel modules.

This would allow mocking drivers tools to not have to muck with
depmod.d config files or assume that your distro will have extra
on a configuration file over built-in.

With today's default you end up actually *crashing* Linux when
trying to load cxl_test with the default "extra" [0] directory being
used. This fixes that and allows other mocking drivers to do
less work.

[0] https://lkml.kernel.org/r/20221209062919.1096779-1-mcgrof@kernel.org

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Acked-by: Dan Williams <dan.j.williams@intel.com>
Acked-by: Masahiro Yamada <masahiroy@kernel.org>
Reviewed-by: Nicolas Schier <nicolas@fjasle.eu>