drm/i915: Print an error message for a reset failure on gen2

Since on gen2, we do not universally have a GPU reset implementation, we
fail i915_reset() at intel_has_gpu_reset(). However, this is also
intentionally disabled for CI testing and so it only has a debug
message. Promote that debug message to a user-facing error message that
should explain why their machine became unusable following the GPU hang.

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171211204040.22858-1-chris@chris-wilson.co.uk