drm/i915: Squash GEM load failure message (again)

Due to a silent conflict (silent because we are trying to fix the CI
test that is meant to exercising these failures!) between commit
51e645b6 ("drm/i915: Mark the GPU as wedged without error on fault
injection") and commit 8571a05a ("drm/i915: Use GEM suspend when
aborting initialisation"), we failed to actually squash the error
message after injecting the load failure.

Rearrange the code to export i915_load_failure() for better logging of
real errors (and quiet logging of injected errors).

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Michał Winiarski <michal.winiarski@intel.com>
Reviewed-by: Michał Winiarski <michal.winiarski@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180609111058.2660-1-chris@chris-wilson.co.uk