[media] st-hva: multi-format video encoder V4L2 driver

This patch adds V4L2 HVA (Hardware Video Accelerator) video encoder
driver for STMicroelectronics SoC. It uses the V4L2 mem2mem framework.

This patch only contains the core parts of the driver:
- the V4L2 interface with the userland (hva-v4l2.c)
- the hardware services (hva-hw.c)
- the memory management utilities (hva-mem.c)

This patch doesn't include the support of specific codec (e.g. H.264)
video encoding: this support is part of subsequent patches.

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>