ARM: 8464/1: Update all mm structures with section adjustments

Currently, when updating section permissions to mark areas RO
or NX, the only mm updated is current->mm. This is working off
the assumption that there are no additional mm structures at
the time. This may not always hold true. (Example: calling
modprobe early will trigger a fork/exec). Ensure all mm structres
get updated with the new section information.

Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Laura Abbott <labbott@fedoraproject.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>