powerpc/64s: Rename hash_hugetlbpage.c to hugetlbpage.c

This file contains functions and data common to radix, so rename it to
remove the hash_ prefix.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211201144153.2456614-11-npiggin@gmail.com