lavc/libopenh264enc: Add coder option to replace cabac

lavc/libopenh264enc: Add coder option to replace cabac

Set DEPRECATED flag to option cabac, replace with coder. The
priority logic is:
1. s->coder; then
2. avctx->coder_type; then
3. s->cabac.

Change the default option to -1 and allow the default cabac to be
determined by profile.

Add FF_API_OPENH264_CABAC macro for cabac to remove this option after
LIBAVCODEC_VERSION_MAJOR = 59.

Reviewed-by: Martin Storsjö <martin@martin.st>
Signed-off-by: Linjie Fu <linjie.fu@intel.com>