target/ppc: Remove RMOR register from POWER9 & POWER10

target/ppc: Remove RMOR register from POWER9 & POWER10

Currently we create the Real Mode Offset Register (RMOR) on all Book3S cpus
from POWER7 onwards.  However the translation mode which the RMOR controls
is no longer supported in POWER9, and so the register has been removed from
the architecture.

Remove it from our model on POWER9 and POWER10.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>