* Xen hypervisor device tree bindings

Xen ARM virtual platforms shall have a top-level "hypervisor" node with
the following properties:

- compatible:
	compatible = "xen,xen-<version>", "xen,xen";
  where <version> is the version of the Xen ABI of the platform.

- reg: specifies the base physical address and size of the regions in memory
  where the special resources should be mapped to, using an HYPERVISOR_memory_op
  hypercall.
  Region 0 is reserved for mapping grant table, it must be always present.
  The memory region is large enough to map the whole grant table (it is larger
  or equal to gnttab_max_grant_frames()).
  Regions 1...N are extended regions (unused address space) for mapping foreign
  GFNs and grants, they might be absent if there is nothing to expose.
  This property is unnecessary when booting Dom0 using ACPI.

- interrupts: the interrupt used by Xen to inject event notifications.
  A GIC node is also required.
  This property is unnecessary when booting Dom0 using ACPI.

To support UEFI on Xen ARM virtual platforms, Xen populates the FDT "uefi" node
under /hypervisor with following parameters:

________________________________________________________________________________
Name                      | Size   | Description
================================================================================
xen,uefi-system-table     | 64-bit | Guest physical address of the UEFI System
                          |        | Table.
--------------------------------------------------------------------------------
xen,uefi-mmap-start       | 64-bit | Guest physical address of the UEFI memory
                          |        | map.
--------------------------------------------------------------------------------
xen,uefi-mmap-size        | 32-bit | Size in bytes of the UEFI memory map
                          |        | pointed to in previous entry.
--------------------------------------------------------------------------------
xen,uefi-mmap-desc-size   | 32-bit | Size in bytes of each entry in the UEFI
                          |        | memory map.
--------------------------------------------------------------------------------
xen,uefi-mmap-desc-ver    | 32-bit | Version of the mmap descriptor format.
--------------------------------------------------------------------------------

Example (assuming #address-cells = <2> and #size-cells = <2>):

hypervisor {
	compatible = "xen,xen-4.3", "xen,xen";
	reg = <0 0xb0000000 0 0x20000>;
	interrupts = <1 15 0xf08>;
	uefi {
		xen,uefi-system-table = <0xXXXXXXXX>;
		xen,uefi-mmap-start = <0xXXXXXXXX>;
		xen,uefi-mmap-size = <0xXXXXXXXX>;
		xen,uefi-mmap-desc-size = <0xXXXXXXXX>;
		xen,uefi-mmap-desc-ver = <0xXXXXXXXX>;
        };
};

The format and meaning of the "xen,uefi-*" parameters are similar to those in
Documentation/arm/uefi.txt in Linux, which are provided by the regular Linux
UEFI stub. However they differ because they are provided by the Xen hypervisor,
together with a set of UEFI runtime services implemented via hypercalls, see
xen/include/public/platform.h.
