ACPI/IORT: Add a helper to retrieve RMR info directly

This will provide a way for SMMU drivers to retrieve StreamIDs
associated with IORT RMR nodes and use that to set bypass settings
for those IDs.

Tested-by: Steven Price <steven.price@arm.com>
Tested-by: Laurentiu Tudor <laurentiu.tudor@nxp.com>
Tested-by: Hanjun Guo <guohanjun@huawei.com>
Reviewed-by: Hanjun Guo <guohanjun@huawei.com>
Signed-off-by: Shameer Kolothum <shameerali.kolothum.thodi@huawei.com>
Acked-by: Robin Murphy <robin.murphy@arm.com>
Link: https://lore.kernel.org/r/20220615101044.1972-6-shameerali.kolothum.thodi@huawei.com
Signed-off-by: Joerg Roedel <jroedel@suse.de>