udev: update udev to new virtual package infra.

The udev virtual package and its current providers (eudev and systemd)
have been updated to use the latest version of virtual package
infrastructure.

A provider should now select BR2_PACKAGE_HAS_UDEV and well as set a
value for BR2_PACKAGE_PROVIDES_UDEV.

Signed-off-by: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>