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>
spapr: limit numa memory regions by ram size

This makes sure that all NUMA memory blocks reside within RAM or
have zero length.

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>