of/address: restrict 'no-ranges' kludge to powerpc

Certain Apple machines don't use the ranges property correctly, but the
workaround should not be applied on other architectures.  This patch
disables the workaround for non-powerpc architectures.

Signed-off-by: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
CC: Stephen Rothwell <sfr@canb.auug.org.au>