arm64: dump: Add checking for writable and exectuable pages

arm64: dump: Add checking for writable and exectuable pages

Page mappings with full RWX permissions are a security risk. x86
has an option to walk the page tables and dump any bad pages.
(See e1a58320a38d ("x86/mm: Warn on W^X mappings")). Add a similar
implementation for arm64.

Reviewed-by: Kees Cook <[email protected]>
Reviewed-by: Mark Rutland <[email protected]>
Tested-by: Mark Rutland <[email protected]>
Signed-off-by: Laura Abbott <[email protected]>
Reviewed-by: Ard Biesheuvel <[email protected]>
[[email protected]: folded fix for KASan out of bounds from Mark Rutland]
Signed-off-by: Catalin Marinas <[email protected]>