[media] st-delta: add mjpeg support

Adds support of DELTA MJPEG video decoder back-end,
implemented by calling JPEG_DECODER_HW0 firmware
using RPMSG IPC communication layer.

Acked-by: Peter Griffin <peter.griffin@linaro.org>
Signed-off-by: Hugues Fruchet <hugues.fruchet@st.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>