libav: add from meta-oe, update and tweak

libav: add from meta-oe, update and tweak

Changes from the meta-oe recipe:
* Update stable recipe to 0.8.8
* Update git recipe to the tag for 9.8 (for now)
* Switch over to a tarball for the release version recipe
* Add LICENSE_FLAGS = "commercial"
* Set SUMMARY instead of DESCRIPTION
* Add yasm-native to DEPENDS since there is now a recipe for it
* Remove libvpx from DEPENDS and add a PACKAGECONFIG option for it,
  disabled by default since it wasn't actually being enabled
* Add a PACKAGECONFIG option for x11 to enable/disable x11grab, and
  add the proper DEPENDS if so (still defaults to enabled)
* Add a number of other PACKAGECONFIG options, replacing some old
  comments as well as offering the ability to disable x264.
* Hide text relocation warning when building for i586 (PIC can't be
  enabled for 32-bit x86).
* Drop PR

Notes for the git recipe:
* This hasn't been able to be built recently in meta-oe since there was
  a circular dependency between libav and libpostproc. libpostproc is
  part of libav 0.8.x but was split out in 9+ and is not needed at all
  anymore by libav itself, so this dependency was removed.
* Additionally the recipe was filtering out the option to enable
  libpostproc but this option wasn't being added by the inc file and
  thus the filter wasn't doing anything, so I dropped this as well.

(From OE-Core rev: 9a670f780b1f1204d426017ff9a95842ad85800e)

Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>