xen/arm: smmuv3: Add support for SMMUv3 driver

xen/arm: smmuv3: Add support for SMMUv3 driver

Add support for ARM architected SMMUv3 implementation. It is based on
the Linux SMMUv3 driver.

Driver is currently supported as Tech Preview.

Major differences with regard to Linux driver are as follows:
2. Only Stage-2 translation is supported as compared to the Linux driver
   that supports both Stage-1 and Stage-2 translations.
3. Use P2M  page table instead of creating one as SMMUv3 has the
   capability to share the page tables with the CPU.
4. Tasklets are used in place of threaded IRQ's in Linux for event queue
   and priority queue IRQ handling.
5. Latest version of the Linux SMMUv3 code implements the commands queue
   access functions based on atomic operations implemented in Linux.
   Atomic functions used by the commands queue access functions are not
   implemented in XEN therefore we decided to port the earlier version
   of the code. Atomic operations are introduced to fix the bottleneck
   of the SMMU command queue insertion operation. A new algorithm for
   inserting commands into the queue is introduced, which is lock-free
   on the fast-path.
   Consequence of reverting the patch is that the command queue
   insertion will be slow for large systems as spinlock will be used to
   serializes accesses from all CPUs to the single queue supported by
   the hardware. Once the proper atomic operations will be available in
   XEN the driver can be updated.
6. Spin lock is used in place of mutex when attaching a device to the
   SMMU, as there is no blocking locks implementation available in XEN.
   This might introduce latency in XEN. Need to investigate before
   driver is out for tech preview.
7. PCI ATS functionality is not supported, as there is no support
   available in XEN to test the functionality. Code is not tested and
   compiled. Code is guarded by the flag CONFIG_PCI_ATS.
8. MSI interrupts are not supported as there is no support available in
   XEN to request MSI interrupts. Code is not tested and compiled. Code
   is guarded by the flag CONFIG_MSI.

Signed-off-by: Rahul Singh <rahul.singh@arm.com>
Reviewed-by: Bertrand Marquis <bertrand.marquis@arm.com>
Reviewed-by: Oleksandr Tyshchenko <oleksandr_tyshchenko@epam.com>
Acked-by: Stefano Stabellini <sstabellini@kernel.org>