powerpc/mm: Fix page table dump build on non-Book3S

In the recent commit 1515ab93 ("powerpc/mm: Dump hash table") we
added code to dump the hage page table. Currently this can be selected
to build on any platform. However it breaks the build if we're building
for a non-Book3S platform, because none of the hash page table related
defines and so on exist. So restrict it to building only on Book3S.

Similarly in commit 8eb07b18 ("powerpc/mm: Dump linux pagetables")
we added code to dump the Linux page tables, which uses some constants
which are only defined on Book3S - so guard those with an #ifdef.

Fixes: 1515ab93 ("powerpc/mm: Dump hash table")
Fixes: 8eb07b18

 ("powerpc/mm: Dump linux pagetables")
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>