[media] st-hva: add H.264 video encoding support

This patch adds the H.264 video encoding capability in the V4L2 HVA
video encoder driver for STMicroelectronics SoC (hva-h264.c).

The main supported features are:
- profile: baseline, main, high, stereo high
- level: up to 4.2
- bitrate mode: CBR, VBR
- entropy mode: CABAC, CAVLC
- video aspect: 1x1 only

Signed-off-by: Yannick Fertre <yannick.fertre@st.com>
Signed-off-by: Jean-Christophe Trotin <jean-christophe.trotin@st.com>
Acked-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>