UPSTREAM: arm64: add support to dump the kernel page tables

In a similar manner to arm, it's useful to be able to dump the page
tables to verify permissions and memory types. Add a debugfs file
to check the page tables.

Acked-by: Steve Capper <steve.capper@linaro.org>
Tested-by: Steve Capper <steve.capper@linaro.org>
Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>
[will: s/BUFFERABLE/NORMAL-NC/]
Signed-off-by: Will Deacon <will.deacon@arm.com>

(cherry picked from commit c9465b4ec37a68425c5a574b56280dc1a7e34070)
Signed-off-by: Tomasz Figa <tfiga@chromium.org>

Bug: 24475017

Change-Id: I7fe213003721e931747baed73fb05194c5fbeb64
Signed-off-by: Kees Cook <keescook@google.com>