drm/i915: Move workaround infrastructure code up

Top comment in intel_workarounds.c says common code should come first so
lets respect that. Also, by moving the common code together opportunities
to reduce duplication will become more obvious.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/1548983324-15344-2-git-send-email-talha.nassar@intel.com