pseries: Add compatible property to root of device tree

pseries: Add compatible property to root of device tree

Currently, for the pseries machine the device tree supplied by qemu to SLOF
and from there to the guest does not include a 'compatible property' at the
root level.  Usually that works fine, since in this case the compatible
property doesn't really give any information not already found in the
'device_type' or 'model' properties.

However, the lack of 'compatible' confuses the bootloader install in the
SLES11 SP2 and SLES11 SP3 installers.  This patch therefore adds a token
'compatible' property to work around that.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Cc: qemu-stable@nongnu.org
Signed-off-by: Alexander Graf <agraf@suse.de>