rockchip: fix boot_devices constants

The DT node name pattern in mmc-controller.yaml for mmc
is "^mmc(@.*)?$". The Rockchip mmc nodes have been synced
with Linux, so update the boot_devices constants as well.

Signed-off-by: Johan Jonker <jbx6244@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>