package/xserver_xorg-server: add blind options to specify driver ABI

The upcoming NVidia Tegra2/3 binary blobs only work with a certain
VIDEODRV ABI (namely up to 14), so we must have a way to represent that
ABI so that such packages can not be enabled with a too recent/old ABI.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>