systemd: Restore mask and preset targets, fix instance creation
Ensure that anyone who sets SYSTEMD_AUTO_ENABLE_${PN} = "mask" (or
"preset") retains the previous behaviour. In addition fix "enable" so it
can (again) create instance units out of templates.
Remove over-zealous quoting of SYSTEMD_SERVICE_ESCAPED as it's already
safely escaped (and can be multiple arguments).
Reported-by: Paul Barker <paul@betafive.co.uk> Signed-off-by: Alex Kiernan <alex.kiernan@gmail.com> Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
