ARM: omap2plus_defconfig: Add support for distros with systemd

Some distros are now using systemd, so let's enable most of
what's recommended at:

http://cgit.freedesktop.org/systemd/systemd/tree/README



Reviewed-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
Signed-off-by: Tony Lindgren <tony@atomide.com>