gst1-vaapi: new package

gst1-vaapi: new package

gstreamer-vaapi consists in a collection of VA-API based plugins for
GStreamer and helper libraries.  These libraries are used for hardware
decoding and encoding of several video formats.

decoding formats:
JPEG, MPEG-2, MPEG-4:2, H.264 AVC, H.264 MVC, VP8, VC-1, WMV3, and HEVC.

encoding formats:
MPEG-2, H.264 AVC, H.264 MVC, JPEG, VP8, HEVC

The package won't compile without at least one renderer enabled, so I
chose to enable DRM by default, as X11, GLX, and wayland are heavy
handed with the dependencies.  As such, I have disabled every option
defaulting to yes except for DRM for the first patch.

Also, these codecs are only for x86 and require a Intel CPU (See Hardware
Requirements on line 82 of the README file.)

Signed-off-by: Adam Duskett <Adamduskett@outlook.com>
[Thomas:
 - Add entry to DEVELOPERS file.
 - Add BR2_TOOLCHAIN_HAS_THREADS dependency to the main Config.in
   option.
 - Add BR2_PACKAGE_HAS_UDEV dependency to the main Config.in option.
 - Add comments about the BR2_STATIC_LIBS config option.
 - Rewrap Config.in help text and removing trailing tabs/spaces.
 - Remove restriction to i386/x86-64
 - Add patch to fix build with uClibc.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>