media: v4l: Add definitions for HEVC stateless decoding

This introduces the required definitions for HEVC decoding support with
stateless VPUs. The controls associated to the HEVC slice format provide
the required meta-data for decoding slices extracted from the bitstream.

They are not exported to the public V4L2 API since reworking this API
will likely be needed for covering various use-cases and new hardware.

Multi-slice decoding is exposed as a valid decoding mode to match current
H.264 support but it is not yet implemented.

The interface comes with the following limitations:
* No custom quantization matrices (scaling lists);
* Support for a single temporal layer only;
* No slice entry point offsets support;
* No conformance window support;
* No VUI parameters support;
* No support for SPS extensions: range, multilayer, 3d, scc, 4 bits;
* No support for PPS extensions: range, multilayer, 3d, scc, 4 bits.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
[hverkuil-cisco@xs4all.nl: use 1ULL in flags defines in hevc-ctrls.h]
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>