libwebp: upgrade 1.2.4 -> 1.3.0

libwebp: upgrade 1.2.4 -> 1.3.0

Changelog:
==========
* add libsharpyuv, which exposes -sharp_yuv/config.use_sharp_yuv
  functionality to other libraries; libwebp now depends on this library
* major updates to the container and lossless bitstream docs (#448, #546,
  #551)
* miscellaneous warning, bug & build fixes (#576, #583, #584)

Signed-off-by: Wang Mingyu <wangmy@fujitsu.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>