[XPKG] Initial support of packager (opkg for now)

This is proof-of-concept of buildng opkg files in Buildroot2 environment

opkg-files magically appears on <fs>/output/xpackage folder
after command 'make <package>-xpackage'

For example, make udev-xpackage will produce
output/xpackage/udev_182_arm.ipk

TODO:
- set correct package dependencies
- extract opkg-build and related stuff to separate files
- options to create pakages in with kconfig