Add --use-vaapi flag to automate.py to enable VAAPI hardware acceleration for videos on Linux

[cztomczak]

It would set the use_vaapi=true GN arg and apply the vaapi patch from archlinux.

In Chromium it seems that the use_vaapi GN arg will enable video acceleration for VP8 and VP9 codecs. Additional acceleration for other codecs/formats (h264, h265, mpeg-4, VC-1) can be enabled by patching ffmpeg.

The vaapi archlinux patch adds enable-accelerated-video flag and includes the libva library (https://github.com/intel/libva).

The archlinux vaapi patch can be found here:
https://aur.archlinux.org/packages/chromium-vaapi/