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