avcodec/nvenc: Add support for H.264 High 444 Predictive encoding

Newer versions of the nvenc hardware support The High 444 Predictive profile
of H.264, and can also do lossless encoding under this profile if desired.

This change introduces support for the profile, and exposes the appropriate
presets for requesting lossless encoding.

I tested lossless by generating a baseline sample with testsrc converted
to raw yuv444p, then encoded the sample with nvenc, then did a framemd5
comparision of both the raw video and the nvenc encode. The framemd5
reports were identical.

Signed-off-by: Philip Langdale <philipl@overt.org>
Signed-off-by: Timo Rothenpieler <timo@rothenpieler.org>
