powerpc: Use of_address_to_resource()

Replace open coded reading of "reg" or of_get_address()/
of_translate_address() calls with a single call to
of_address_to_resource().

Signed-off-by: Rob Herring <robh@kernel.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230329220337.141295-1-robh@kernel.org