powerpc/mm: Move radix/hash common data structures to book3s64 headers

Start moving code that is generic between radix and hash to book3s64
specific headers from the book3s64 hash specific one.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>