phy: Move phy-rockchip-dphy-rx0 out of staging

There is no need for this driver to be in staging.
Let's promote it!

Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Link: https://lore.kernel.org/r/20200825220710.634106-1-ezequiel@collabora.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>