[PATCH] Tweak encoding options for VP9

[PATCH] Tweak encoding options for VP9

Don't set both bitrate and CRF, as they are conflicting settings.
Instead only set CRF. Also enable row-mt and avoid modifying the codec
context in a function that is about options.

Gbp-Pq: Name upstream_123ae0d2_Tweak-encoding-options-for-VP9.patch