media: cedrus: Allow different mod clock rates

Some VPU variants may run at higher clock speeds. They actually need
extra speed to be capable of decoding more complex codecs like HEVC or
bigger image sizes (4K).

Expand variant structure with mod_rate information.

Signed-off-by: Jernej Skrabec <jernej.skrabec@siol.net>
Acked-by: Maxime Ripard <maxime.ripard@bootlin.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>