For devices connecting to an ITS, the devices need to identify themself
through a devid; this devid is represented in the IORT table in named
component node [1] for platform devices, so this patch adds code that
scans the IORT table to retrieve the devices devid.

Add an IORT interface to collect ITS devices devid to carry out platform
devices MSI mappings with IORT tables.

[1]: https://static.docs.arm.com/den0049/b/DEN0049B_IO_Remapping_Table.pdfSigned-off-by: NHanjun Guo <hanjun.guo@linaro.org>
[lorenzo.pieralisi@arm.com: rewrote commit log/dropped ITS changes]
Signed-off-by: NLorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Tested-by: NMing Lei <ming.lei@canonical.com>
Tested-by: NWei Xu <xuwei5@hisilicon.com>
Tested-by: NSinan Kaya <okaya@codeaurora.org>
Cc: Marc Zyngier <marc.zyngier@arm.com>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Tomasz Nowicki <tn@semihalf.com>
Cc: Thomas Gleixner <tglx@linutronix.de>