update-rcd.bbclass: handle both sysvinit and systemd features being present

update-rcd.bbclass: handle both sysvinit and systemd features being present

Run the helper if the sysvinit feature is present, or if the systemd feature is
present but the systemd class hasn't been inherited.  We want to run in the
latter case as systemd has sysvinit compatibility, but we don't want to always
run so that pure systemd images don't have redundant sysvinit files.

(From OE-Core rev: a3856ab19f1d4ae312f559521785ad4384700729)

Signed-off-by: Ross Burton <ross.burton@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>