The STM32MP DDR Controller has a very flexible way of mapping address
bits to columns/rows/banks. This is so far configured by the ARM TF-A
as part of the SDRAM setup, so we don't need to do this in barebox.

Nevertheless reading it out in barebox, allows us to determine unused
address bits and thus the total size of SDRAM configured.

Add a simple driver that parses the ddrctrl node and adds an appropriate
memory bank. This can later be used to remove explicit calls to
arm_add_mem_device in board code.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>