spapr/rtas: Reserve space for RTAS blob and log

spapr/rtas: Reserve space for RTAS blob and log

At the moment SLOF reserves space for RTAS and instantiates the RTAS blob
which is 20 bytes binary blob calling an hypercall. The rest of the RTAS
area is a log which SLOF has no idea about but QEMU does.

This moves RTAS sizing to QEMU and this overrides the size from SLOF.
The only remaining problem is that SLOF copies the number of bytes it
reserved (2KB for now) so QEMU needs to reserve at least this much;
SLOF will be fixed separately to check that rtas-size from QEMU is
enough for those 20 bytes for the H_RTAS hcall.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Message-Id: <20200316011841.99970-1-aik@ozlabs.ru>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>