hevc: compact ff_hevc_luma_mv_mvp_mode

LX can be either 0 or 1.

Conflicts:
	libavcodec/hevc_mvs.c
hevc: unlispify ff_hevc_luma_mv_mvp_mode

Conflicts:
	libavcodec/hevc_mvs.c
hevc: use macros to simplify

Conflicts:
	libavcodec/hevc_mvs.c