This multiboot support will be built in linux module for aarch64, and can not be used alone.

- the implementation for Xen is following <Multiboot on ARM Specification>: http://wiki.xen.org/wiki/Xen_ARM_with_Virtualization_Extensions/Multiboot and xen/docs/misc/arm/device-tree/booting.txt in Xen source code.

- Add multiboot command for loading multiboot kernel image. Usage: multiboot <the path of kernel image file> [cmdline]

- Add module command for loading multiboot module. Usage: module [option] <the path of module file> [cmdline]

The [option] for Xen is [--type <compatible stream in FDT>]. For now, the <compatible stream in FDT> could be : "multiboot,kernel", "multiboot,ramdisk", "multiboot,module", "xen,xsm-policy" or the custom compatible stream

- Only support stub-kernel for arm64: support stub-kernel detection and alignment info detection

- The reason of adding this functionality to the existing "linux" module rather than "multiboot(2)" (1)multiboot is x86 only (2)Multiboot is added to "linux" module because it reuses existing code.

- Some changes in original linux module code Move some #define from grub-core/loader/arm64/linux.c to include/grub/arm64/linux.h Reason: (1)make code more orderly (2)these #define can be used by other files which includs include/grub/arm64/linux.h Export some accessor functions of dtb and the "loaded" flag for sharing code to multiboot.c

Signed-off-by: Fu Wei fu.wei@linaro.org