package/openrc: new package

package/openrc: new package

This adds openrc init system package. This performs default openrc
installation with openrc-init that acts as pid1.

MKPKGCONFIG=no:
openrc does not use pkg-config per se, if MKPKGCONFIG is enabled,
it will just install *.pc files on rootfs for other programs to
find librc and libeinfo. These libs expose C api to control openrc
(al rc-* functions use it). From the looks of it, these libs would
be usefull if user wanted to write his own programs to manage
services, and vast majority of people using openrc won't need it.
Also, that's the reason why there is not INSTALL_STAGING=yes.

Signed-off-by: Michał Łyszczek <michal.lyszczek@bofc.pl>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>