pseries: Allow RTAS tokens without a qemu handler

pseries: Allow RTAS tokens without a qemu handler

Kernel-based RTAS calls will not have a qemu handler, but will
still be registered in qemu in order to be assigned a token
number and appear in the device-tree.

Let's test for the name being NULL rather than the handler
when deciding to skip an entry while building the device-tree

Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Signed-off-by: Alexander Graf <agraf@suse.de>