ppc/pnv: Add HIOMAP commands

ppc/pnv: Add HIOMAP commands

This activates HIOMAP support on the QEMU PowerNV machine. The PnvPnor
model is used to access the flash contents. The model simply maps the
contents at a fix offset and enables or disables the mapping.

HIOMAP Protocol description :

  https://github.com/openbmc/hiomapd/blob/master/Documentation/protocol.md

Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20191028070027.22752-3-clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>