introduce mbus DRAM target info abstraction

Introduce struct mbus_dram_target_info, which will be used for
passing information about the mbus target ID of the DDR unit, and
mbus target attribute, base address and size for each of the DRAM
chip selects from the platform code to peripheral drivers.

Signed-off-by: Lennert Buytenhek <buytenh@marvell.com>
Reviewed-by: Tzachi Perelstein <tzachi@marvell.com>
Acked-by: Russell King <rmk+kernel@arm.linux.org.uk>
Signed-off-by: Nicolas Pitre <nico@marvell.com>