nvidia-detect: add functionality to check Xorg ABI

Add functionality to check Xorg ABI.

This patch adds two functions to get the Xorg Server ABI and check if it
is supported by the NVIDIA driver appropriate for the hardware detected.

This will allow end users to check if the NVIDIA driver supports the
currently installed Xorg Server.

Signed-off-by: Philip J Perry <phil@elrepo.org>