The ppc_radix64_walk_tree() routine walks through the nested radix
tables to look for a PTE.

Split it in two and introduce a new routine ppc_radix64_next_level()
which we will use for partition-scoped Radix translation when
translating the process tree addresses. The prototypes are slightly
change to use a 'AddressSpace *' parameter, instead of a 'PowerPCCPU *'
which is not required, and to return an error code instead of a PTE
value. It clarifies error handling in the callers.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Greg Kurz <groug@kaod.org>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20200403140056.59465-4-clg@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>