systemd.bbclass: Dont use libdir and base_libdir for units

systemd.bbclass: Dont use libdir and base_libdir for units

systemd always uses /lib and /usr/lib to store unit files
so using libdir and base_libdir is incorrect. It will work
where libdir is usr/lib and base_libdir is /lib but wont work
when say its /lib64

Add a check to make sure that SYSTEMD_PACKAGES are part of PACKAGES
too, otherwise error out

(From OE-Core rev: 22e16f44b58ae6bbf719b9074d39aac065a402f1)

Signed-off-by: Khem Raj <raj.khem@gmail.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>