package/nvidia-driver: CUDA support does not require X.org

Currently, nvidia-driver always installs the X.org driver, assuming this
is a requirement for all functionalities provided by nvidia-driver, thus
pulling in quite a bunch of X.org packages.

However, it is perfectly legit to be doing CUDA (and OpenCL) work
without the full X.org stack, and indeed the NVidia CUDA and OpenCL
libraries do not require the X.org stack.

Split the configuration so that it is posible to install the different
parts independently from each others, so that CUDA can be installed all
on its own.

Reported-by: Al West <al.west@v-nova.com>
Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Al West <al.west@v-nova.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>