media: v4l2-ctrls: Add sps_rps_extended control

The vdpu381 decoder found on newer Rockchip SoC need the information
from the long term and short term ref pic sets from the SPS.

So far, it wasn't included in the v4l2 API, so add it with a new dynamic
sized control.

Each element of the array contains the long term and short term ref pic
set at that index.

Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>