-rt kernel support

[Andreas Beckmann]

Hi Luca,

384.xx re-adds the PREEMPT_RT sanity check. (upstream changelog:
"Restored several sanity checks that were inadvertently removed from the
kernel module build process in the 355.06 driver")
We had disabled that check in 340.xx "since we had always disabled it",
but I'm not sure whether that is actually a good idea if upstream says
"this does not work". So I'm rather thinking about keeping that check
(and excluding -rt kernels from being tested in build-module-packages.sh).
There might have been reports from people saying that the nvidia driver
worked for them on -rt kernels in the past.
What do you think?

Andreas