drm/i915/selftests: Add coverage of mocs registers

Probe the mocs registers for new contexts and across GPU resets. Similar
to intel_workarounds, we have tables of what register values we expect
to see, so verify that user contexts are affected by them. In the
future, we should add tests similar to intel_sseu to cover dynamic
reconfigurations.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Prathap Kumar Valsan <prathap.kumar.valsan@intel.com>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Prathap Kumar Valsan <prathap.kumar.valsan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191112223600.30993-4-chris@chris-wilson.co.uk