ppc4xx_sdram: Convert DDR SDRAM controller to new bank handling

ppc4xx_sdram: Convert DDR SDRAM controller to new bank handling

Use the generic bank handling introduced in previous patch in the DDR
SDRAM controller too. This also fixes previously broken region unmap
due to sdram_ddr_unmap_bcr() ignoring container region so it crashed
with an assert when the guest tried to disable the controller.

Signed-off-by: BALATON Zoltan <balaton@eik.bme.hu>
Message-Id: <fc7c50e365d0027a659111e9cd67f9b93113a163.1666194485.git.balaton@eik.bme.hu>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>