drm/i915: Ironlake do_idle_maps w/a may be called w/o struct_mutex

drm/i915: Ironlake do_idle_maps w/a may be called w/o struct_mutex

Since commit 1233e2db199d ("drm/i915: Move object backing storage
manipulation to its own locking"), i915_gem_object_put_pages() and
specifically the i915_gem_gtt_finish_pages() may be called from outside
of the struct_mutex and so we can no longer pass I915_WAIT_LOCKED to
i915_gem_wait_for_idle.

Fixes: 1233e2db199d ("drm/i915: Move object backing storage manipulation to its own locking")
Signed-off-by: Chris Wilson <[email protected]>
Cc: Chris Wilson <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: Daniel Vetter <[email protected]>
Cc: Jani Nikula <[email protected]>
Cc: [email protected]
Cc: <[email protected]> # v4.10+
Link: http://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Joonas Lahtinen <[email protected]>