We're finally getting CRC support in nouveau, so let's start testing
this in igt as well! While the normal CRC capture tests are nice,
there's a number of Nvidia-specific hardware characteristics that we
need to test as well.

The most important one is known as a "notifier context flip". Basically,
Nvidia GPUs store generated CRCs in an allocated memory region, referred
to as the notifier context, that the driver programs itself. Strangely,
this region can only hold a limited number of CRC entries, and once it
runs out of available entries the hardware simply sets an overrun bit
and stops writing any new CRC entries.

Since igt-gpu-tools doesn't really have an expectation of only being
able to grab a limited number of CRCs, we work around this in nouveau by
allocating two separate CRC notifier regions each time we start
capturing CRCs, and then flip between them whenever we get close to
filling our currently programmed notifier context. While this keeps the
number of CRC entri...