media: allegro: add HEVC NAL unit generator

When encoding a video as HEVC, the allegro driver needs to generate the
Non-VCL NAL units for HEVC. Do the same as for H.264 and add a module
that takes C structs for the VPS/SPS/PPS and encodes the fields as RBPS
as specified by "ITU-T Rec. H.265 (02/2018) high efficiency video
coding".

[hverkuil: add missing static for nal_hevc_write/read_start_code_prefix]
[hverkuil: fix typo: pps -> vps in nal_hevc_write_vps]

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+huawei@kernel.org>

media: allegro: extract RBSP handler from H.264 NAL generator

The RBSP structure is the same for HEVC and H.264. In order to be able
to reuse the RBSP handler for generating HEVC NAL units, extract the
functions from the H.264 generator.

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+huawei@kernel.org>

media: allegro: move driver out of staging

The stateful encoder API was finalized. Nothing is blocking the driver
from being moved out of staging.

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+huawei@kernel.org>