You can run ffmpeg -h encoder=libx264
and look for values of supported pixel formats.
For bit-depth=8 of libx264 it will be something like:
Supported pixel formats: yuv420p yuvj420p yuv422p yuvj422p yuv444p yuvj444p nv12 nv16
And for bit-depth=10 of libx264 it will be something like:
Supported pixel formats: yuv420p10le yuv422p10le yuv444p10le nv20le