media: dt-bindings: media: Add vendor prefix for allegro

Add vendor prefix for Allegro DVT, a provider of H.264/AVC, H.265/HEVC,
AVS2, VP9 and AV1 compliance test suites and H.264/AVC, H.265/HEVC, and
VP9 encoder, codec and decoder hardware (RTL) IPs.

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