drm/i915: Re-enable GGTT earlier after GPU reset

Inside i915_gem_reset(), we start touching the HW and so require the
low-level HW to be re-enabled, in particular the PCI BARs.

Fixes: 7b6da818 ("drm/i915: Restore the kernel context after a GPU reset on an idle engine")
References: 0db8c961 ("drm/i915: Re-enable GTT following a device reset")
Testcase: igt/drv_hangman #i915g/i915gm
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Michel Thierry <michel.thierry@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20171217132852.30642-1-chris@chris-wilson.co.ukReviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

drivers/gpu/drm/i915/i915_drv.c

@@ -1924,9 +1924,6 @@ void i915_reset(struct drm_i915_private *i915, unsigned int flags)
 		goto taint;
 	}
 
-	i915_gem_reset(i915);
-	intel_overlay_reset(i915);
-
 	/* Ok, now get things going again... */
 
 	/*
@@ -1939,6 +1936,9 @@ void i915_reset(struct drm_i915_private *i915, unsigned int flags)
 		goto error;
 	}
 
+	i915_gem_reset(i915);
+	intel_overlay_reset(i915);
+
 	/*
 	 * Next we need to restore the context, but we don't use those
 	 * yet either...