ACPI / tables: Add IORT to injectable table list

Loading IORT table from initrd can be used to fix severe firmware
IORT defects temporarily before platform/BIOS vendor releases an
upgraded BIOS binary.

Moreover, it is very powerful to debug SMMU node/device probe, MSI
allocation, stream id translation and IORT table from firmware.

It is also very useful to enable SMMU and devices behind SMMU before
firmware is ready.

This patch adds ACPI_SIG_IORT to the table, which enables IORT
from initrd to override which from firmware.

Signed-off-by: Yang Shunyong <shunyong.yang@hxt-semitech.com>
Acked-by: Hanjun Guo <hanjun.guo@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>