media: allegro: add Allegro DVT video IP core driver

Add a V4L2 mem-to-mem driver for Allegro DVT video IP cores as found in
the EV family of the Xilinx ZynqMP SoC. The Zynq UltraScale+ Device
Technical Reference Manual uses the term VCU (Video Codec Unit) for the
encoder, decoder and system integration block.

This driver takes care of interacting with the MicroBlaze MCU that
controls the actual IP cores. The IP cores and MCU are integrated in the
FPGA. The xlnx_vcu driver is responsible for configuring the clocks and
providing information about the codec configuration.

The driver currently only supports the H.264 video encoder.

Signed-off-by: Michael Tretter <m.tretter@pengutronix.de>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>