target/ppc: Introduce ppc_radix64_xlate() for Radix tree translation

This is moving code under a new ppc_radix64_xlate() routine shared by
the MMU Radix page fault handler and the 'get_phys_page_debug' PPC
callback. The difference being that 'get_phys_page_debug' does not
generate exceptions.

The specific part of process-scoped Radix translation is moved under
ppc_radix64_process_scoped_xlate() in preparation of the future support
for partition-scoped Radix translation. Routines raising the exceptions
now take a 'cause_excp' bool to cover the 'get_phys_page_debug' case.

It should be functionally equivalent.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@gmail.com>
Signed-off-by: Cédric Le Goater <clg@kaod.org>
Message-Id: <20200403140056.59465-2-clg@kaod.org>
Reviewed-by: Greg Kurz <groug@kaod.org>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>