ARM: configs: keystone: Add basic systemd related options

Add basic options to bootup on systemd based distros such as debian.
See http://cgit.freedesktop.org/systemd/systemd/tree/README#n38

 for
more information.

Signed-off-by: Nishanth Menon <nm@ti.com>
Signed-off-by: Santosh Shilimkar <ssantosh@kernel.org>