arm64: Add Xen boot support (via fdt)

From: Fu Wei <[email protected]>

- This adds support for the Xen boot on ARM specification for arm64.

- Add and export some accessor functions of "loaded" flag and grub_linux_get_fdt function in include/grub/arm64/linux.h for xen boot.

- Introduce xen_hypervisor, xen_linux, xen_initrd and xen_xsm to load different binaries for xen boot.
Introduce xen_module to load common or custom module for xen boot.

- This Xen boot support is a separated module for aarch64, but reuse the existing code of devicetree in linux module.

- Add the support of xen_hypervisor, xen_linux and xen_initrd

    in util/grub.d/20_linux_xen.in

- Add the introduction of all xen boot commands in docs/grub.texi

- The example of this support is <How to boot Xen with GRUB on AArch64 the Foundation FVP model>
https://wiki.linaro.org/LEG/Engineering/Grub2/Xen_booting_on_Foundation_FVP_model_by_GRUB

Changelog:
v3: create separate module for xen boot: xen_boot
create separate commands for different types of module delete order-dependent for commands of xen module simplify the code

v2: remove the patches which have been accepted.
according to Vladimir's suggestion, change the command manes and relevant code:
multiboot-->xen_hypervisor
module-->xen_module
improve the option parsing support for xen_hypervisor/xen_module commands. add a patch for adding xen_hypervisor/xen_module support
in util/grub.d/20_linux_xen.in.
update docs/grub.texi patch for the new command names.

v1: The first version upstream patchset to grub-devel mailing list

Fu Wei (4):
arm64: Add and export some accessor functions for xen boot
arm64: Add xen_boot module file
* util/grub.d/20_linux_xen.in: Add support of the XEN boot on aarch64
arm64: Add the introduction of xen boot commands in docs/grub.texi

 docs/grub.texi                    |  56 ++++
 grub-core/Makefile.core.def       |   7 +
 grub-core/loader/arm64/linux.c    |  13 +
 grub-core/loader/arm64/xen_boot.c | 685 ++++++++++++++++++++++++++++++++++++++
 include/grub/arm64/linux.h        |   6 +-
 util/grub.d/20_linux_xen.in       |  16 +-
 6 files changed, 779 insertions(+), 4 deletions(-)
 create mode 100644 grub-core/loader/arm64/xen_boot.c

1.8.3.1