powerpc/mm/radix: Free PUD table when freeing pagetable

remove_pagetable() isn't freeing PUD table. This causes memory
leak during memory unplug. Fix this.

Fixes: 4b5d62ca ("powerpc/mm: add radix__remove_section_mapping()")
Signed-off-by: Bharata B Rao <bharata@linux.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20200709131925.922266-3-aneesh.kumar@linux.ibm.com