media: rkvdec: Support per-variant interrupt handler

media: rkvdec: Support per-variant interrupt handler

Prepare for supporting different variants with different interrupt
managers.

To support other variants specific function type later, introduce the
rkvdec_variant_ops struct.

Tested-by: Diederik de Haas <didi.debian@cknow.org>  # Rock 5B
Reviewed-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>
Signed-off-by: Nicolas Dufresne <nicolas.dufresne@collabora.com>
Signed-off-by: Hans Verkuil <hverkuil+cisco@kernel.org>