drm/i915: Taint (TAINT_WARN) the kernel if the GPU reset fails

drm/i915: Taint (TAINT_WARN) the kernel if the GPU reset fails

History tells us that if we cannot reset the GPU now, we never will. This
then impacts everything that is run subsequently. On failing the reset,
we mark the driver as wedged, trying to prevent further execution on the
GPU, forcing userspace to fallback to using the CPU to update its
framebuffers and let the user know what happened.

We also want to go one step further and add a taint to the kernel so that
any subsequent faults can be traced back to this failure. This is
useful for CI, where if the GPU/driver fails we want to reboot and
restart testing rather than continue on into oblivion. For everyone
else, the warning taint is a testament to the system unreliability.

TAINT_WARN is used anytime a WARN() is emitted, which is suitable for
our purposes here as well; the driver/system may behave unexpectedly
after the failure.

v2: Also taint if the recovery fails (again history shows us that is
typically fatal).
v3: Use TAINT_WARN

References: https://bugs.freedesktop.org/show_bug.cgi?id=103514
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Acked-by: Tomi Sarvela <tomi.p.sarvela@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171205172757.32609-1-chris@chris-wilson.co.uk