Enable VPx encoder ; change video-output file format to mp4

based on this commits:

https://github.com/MoKee/android_device_samsung_p5100/commit/07ef6d783c549527e9cc2ecfd9e99be5d60b82dc

https://github.com/andi34/android_device_samsung_p5100/commit/43c3ee317ea247c25544b3b959b62ecd5dcb5cd8

https://github.com/MoKee/android_device_samsung_p5100/commit/da346ad26da5a4a4cf288cb0a6e3b95c5554d3d2

https://github.com/MoKee/android_device_samsung_p5100/commit/a19385201f8c15b4f1e73df6f6bcfea794132435