dt-bindings: clock: sunxi: Export CLK_DRAM for devfreq

The MBUS node needs to reference the CLK_DRAM clock, as the MBUS
hardware implements memory dynamic frequency scaling using this clock.

Export this clock for SoCs which will be getting a devfreq driver.

Acked-by: Rob Herring <robh@kernel.org>
Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://lore.kernel.org/r/20211118031841.42315-2-samuel@sholland.org