lavu/opt: extend AVOptionRange by extra values

AVOptionRange is not flexible enough to store AV_OPT_TYPE_IMAGE_SIZE
ranges. Current implementation can only store pixel count.
This patch aims to keep backward compatibility and extend
AVOptionRange with possibility to store width/height ranges.

Signed-off-by: Lukasz Marek <lukasz.m.luki@gmail.com>
Merge commit 'lukaszmluki/master^'

* commit 'lukaszmluki/master^':
  lavu/opt: extend AVOptionRange by extra values

Merged-by: Michael Niedermayer <michaelni@gmx.at>