ARM: 8737/1: mm: dump: add checking for writable and executable

Page mappings with full RWX permissions are a security risk.
x86, arm64 has an option to walk the page tables
and dump any bad pages.

(1404d6f1
("arm64: dump: Add checking for writable and exectuable pages"))
Add a similar implementation for arm.

Reviewed-by: Kees Cook <keescook@chromium.org>
Tested-by: Laura Abbott <labbott@redhat.com>
Reviewed-by: Laura Abbott <labbott@redhat.com>
Signed-off-by: Jinbum Park <jinb.park7@gmail.com>
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>