spapr: make sure RMA is in first mode of first memory node

spapr: make sure RMA is in first mode of first memory node

The SPAPR specification says that the RMA starts at the LPAR's logical
address 0 and is the first logical memory block reported in
the LPAR’s device tree.

So SLOF only maps the first block and that block needs to span
the full RMA.

This makes sure that the RMA area is where SLOF expects it.

Reviewed-by: Thomas Huth <thuth@linux.vnet.ibm.com>
Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Alexander Graf <agraf@suse.de>