drm/nouveau/ce/gk104: attempt at better handling of LAUNCHERR

Very rough, no idea how correct it is at this point, but it prevents
getteximage-depth from piglit from hanging the GPU.

v2: updated with NV_PCE_FE_LAUNCHERR_REPORT values provided by NVIDIA

Signed-off-by: Ben Skeggs <bskeggs@redhat.com>