arm64: mvebu: a8k: autodetect RAM size

arm64: mvebu: a8k: autodetect RAM size

Some Armada 8K boards like Macchiatobin and Clearfog GT-8K use RAM from
external DIMM. Hard coding the RAM size in the device-tree is not
convenient. Fortunately, the ATF that initializes the RAM knows the size
of RAM, and U-Boot can query the ATF using a SMC call.

The ATF maps the lower 3G of RAM starting at address 0. Higher RAM is
mapped at 4G. This leaves a 1G hole between 3G and 4G for IO
peripherals. Use a second bi_dram[] entry to describe the higher RAM
area. As a result, CONFIG_NR_DRAM_BANKS must be set to 2 to use more
than 3GB RAM.

This code in this commit is mostly taken from downstream Marvell U-Boot
code by Grzegorz Jaszczyk.

Cc: Grzegorz Jaszczyk <jaz@semihalf.com>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Stefan Roese <sr@denx.de>