aspeed: Set the dram container at the SoC level

Currently, the Aspeed machines allocate a ram container region in
which the machine ram region is mapped. See commit ad1a9782
("aspeed: add a RAM memory region container"). An extra region is
mapped after ram in the ram container to catch invalid access done by
FW. That's how FW determines the size of ram. See commit ebe31c0a
("aspeed: add a max_ram_size property to the memory controller").

Let's move all the logic under the SoC where it should be. It will
also ease the work on multi SoC support.

Reviewed-by: Peter Delevoryas <pdel@fb.com>
Message-Id: <20220623202123.3972977-1-clg@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>