acpi: Disable ACPI table override if securelevel is set

acpi: Disable ACPI table override if securelevel is set

From the kernel documentation (initrd_table_override.txt):

  If the ACPI_INITRD_TABLE_OVERRIDE compile option is true, it is possible
  to override nearly any ACPI table provided by the BIOS with an
  instrumented, modified one.

When securelevel is set, the kernel should disallow any unauthenticated
changes to kernel space. ACPI tables contain code invoked by the kernel, so
do not allow ACPI tables to be overridden if securelevel is set.

Signed-off-by: Linn Crosetto <linn@hpe.com>
[bwh: Forward-ported to 4.7: ACPI override code moved to drivers/acpi/tables.c]
[bwh: Forward-ported to 4.9: adjust context]

Gbp-Pq: Topic features/all/securelevel
Gbp-Pq: Name acpi-disable-acpi-table-override-if-securelevel-is-s.patch