mtd: phram,slram: Disable when the kernel is locked down

mtd: phram,slram: Disable when the kernel is locked down

These drivers allow mapping arbitrary memory ranges as MTD devices.
This should be disabled to preserve the kernel's integrity when it is
locked down.

* Add the HWPARAM flag to the module parameters
* When slram is built-in, it uses __setup() to read kernel parameters,
  so add an explicit check security_locked_down() check

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Cc: Matthew Garrett <mjg59@google.com>
Cc: David Howells <dhowells@redhat.com>
Cc: Joern Engel <joern@lazybastard.org>
Cc: linux-mtd@lists.infradead.org
Gbp-Pq: Topic features/all/lockdown
Gbp-Pq: Name mtd-disable-slram-and-phram-when-locked-down.patch