BugLink: http://bugs.launchpad.net/bugs/1614309

When trying to boot large kernel and initrd images on large systems
(with hundreds of CPUs and Terabytes of memory), we sometimes run out
of memory for the flattened device tree (FDT).

Increase the memory allocated for the Real Mode Area (RMA) to 512MB to
allow more room for the FDT.
Signed-off-by: Sukadev Bhattiprolu <sukadev@linux.vnet.ibm.com>
Signed-off-by: Tim Gardner <tim.gardner@canonical.com>
Acked-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kamal Mostafa <kamal@canonical.com>