Add basic read/write support for the ESB cache configuration register
on P10. We don't model the ESB cache in qemu so reading/writing the
register won't do anything, but it avoids logging a guest error when
skiboot configures it:

qemu-system-ppc64 -machine powernv10 ... -d guest_errors
      ...
XIVE[0] - VC: invalid read @240
XIVE[0] - VC: invalid write @240

Signed-off-by: Frederic Barrat <fbarrat@linux.ibm.com>
Reviewed-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20230601121331.487207-3-fbarrat@linux.ibm.com>
Signed-off-by: Daniel Henrique Barboza <danielhb413@gmail.com>