powerpc: Move page table dump files in a dedicated subdirectory

[ Upstream commit e66c3209c7fd17209ccc4cbbee8b1b1bd5c438dd ]

This patch moves the files related to page table dump in a
dedicated subdirectory.

The purpose is to clean a bit arch/powerpc/mm by regrouping
multiple files handling a dedicated function.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[mpe: Shorten the file names while we're at it]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Stable-dep-of: 66b2ca086210 ("powerpc/64s/radix: Fix soft dirty tracking")
Signed-off-by: Sasha Levin <sashal@kernel.org>