drm/i915/selftests: Take rpm wakeref around partial tiling tests

drm/i915/selftests: Take rpm wakeref around partial tiling tests

Since the partial tiling tests are poking into the GGTT to watch the
fence registers in operation, it itself needs the device rpm wakeref in
order for the GGTT to remain accessible.

Signed-off-by: Chris Wilson <[email protected]>
Cc: Joonas Lahtinen <[email protected]>
Cc: Mika Kuoppala <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Reviewed-by: Matthew Auld <[email protected]>