When used as a BMC, the host expects to be able to use 16MB of
framebuffer memory at the top of RAM.
Signed-off-by: NCyril Bur <cyrilbur@gmail.com>
Signed-off-by: NJoel Stanley <joel@jms.id.au>

A common device tree for all forth gen/ast2400 systems and a board
specific dts for the Palmetto OpenPower developemnt machine which was
used for testing.
Signed-off-by: NJoel Stanley <joel@jms.id.au>