MFC r293835:

Improve non-interactive forth cmd error reporting

Sponsored by: Multiplay

MFC r286234 (by trasz):

Fix a problem which made loader(8) load non-kld files twice.

Sponsored by: Multiplay

MFC r281169, r293724, r293796, r294029, r294041, r294058

MFC r281169 (by andrew):
Make global variabled only used in this file static

MFC r294058:
Make common boot file_loadraw name parameter const

MFC r294041:
Remove unused reg param from fdt_fixup_memory

MFC r293724:
Enable warnings in EFI boot code

MFC r293796:
Fix typo in libefi.c

MFC r294029:
Only build EFI components on supported compilers

Sponsored by: Multiplay

MFC r277215, r277291, r277418, r280953 and r280954:

loader: implement multiboot support for Xen Dom0

Note that only the subset of the multiboot specification needed in order to
boot a Xen Dom0 is implemented.

Sponsored by: Citrix Systems R&D

MFC r271054:

When built with FDT support, add /boot/dtb to the list of search directories.

MFC r262340, r262345, r262347, find and load an appropriate dtb file.

The search order for a usable dtb in fdt_setup_fdtp() is now

- A dtb loaded with an explicit "load -t dtb" command.
- A dtb already loaded into memory somehow[*] and pointed to by fdt_to_load.
- A dtb in the memory pointed to by the u-boot env vars fdtaddr or fdt_addr.
- A file named by the u-boot env vars fdtfile or fdt_file.
- A static dtb compiled into the kernel.

* Presumably by some arch-specific command or code.

MFC r271054:

When built with FDT support, add /boot/dtb to the list of search directories.

MFC r262340, r262345, r262347, find and load an appropriate dtb file.

The search order for a usable dtb in fdt_setup_fdtp() is now

- A dtb loaded with an explicit "load -t dtb" command.
- A dtb already loaded into memory somehow[*] and pointed to by fdt_to_load.
- A dtb in the memory pointed to by the u-boot env vars fdtaddr or fdt_addr.
- A file named by the u-boot env vars fdtfile or fdt_file.
- A static dtb compiled into the kernel.

* Presumably by some arch-specific command or code.