target/ppc: Rework ppc_radix64_walk_tree() for partition-scoped translation

target/ppc: Rework ppc_radix64_walk_tree() for partition-scoped translation

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 <[email protected]>
Signed-off-by: Greg Kurz <[email protected]>
Signed-off-by: Cédric Le Goater <[email protected]>
Message-Id: <20200403140056[email protected]>
Signed-off-by: David Gibson <[email protected]>