[media] v4l2: Add VP8 QP min and max controls

The QP range is specific to every codec. These controls enable
VP8 drivers to define the supported range.

Change-Id: I7990aea15034776a33ae54699add244d694bf4ca
CRs-Fixed: 578892
Signed-off-by: Jorge Solano Altamirano <jsolano@codeaurora.org>