pkgconf: add recipe

pkgconf: add recipe

pkgconf is a better replacement for pkg-config. Fedora 26 replaces the
system pkg-config implementation with pkgconf because it "provides better
support for handling .pc files and a stable library ABI/API for integrating
into applications." and is actively maintained, unlike pkg-config.

pkgconf aims to offer many improvements over pkg-config such as faster/more
efficient dependency resolver which "allows for the user to more conservatively
link their binaries -- which may be helpful in some environments, such as when
prelink(1) is being used.

pkgconf also aims to provide a more complete implementation of pkg-config.
The features most likely to benefit the Yocto Project build system are the
faster/more efficient dependency resolution and linker flag optimisation.

Move pkgconf recipe to oe-core from meta-pkgconf:
https://github.com/kergoth/meta-kergoth-wip/tree/master/meta-pkgconf

Links:
1. http://pkgconf.org
2. https://fedoraproject.org/wiki/Changes/pkgconf_as_system_pkg-config_implementation
3. https://bugzilla.yoctoproject.org/show_bug.cgi?id=11308

Signed-off-by: Christopher Larson <chris_larson@mentor.com>
Signed-off-by: Maxin B. John <maxin.john@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>