rockchip: Pinephone Pro: Add DDR RAM type config

Add the RAM_ROCKCHIP_LPDDR4 to fix the Pinephone Pro booting.
When the configs were updated in 26f92be0 it somehow broke
the PPP boot process so let's fix it.

Signed-off-by: Peter Robinson <pbrobinson@gmail.com>
CC: Jagan Teki <jagan@edgeble.ai>
CC: Kever Yang <kever.yang@rock-chips.com>