MFC r295356 (Partial)

Fix EFI platform build failures on arm.armeb

Approved by: re (marius)
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 r277962, r277988, r282661, r282727, r282731, r283013, r283035:

Add support for booting relocatable kernels on PowerPC.

Add code to support loading relocatable kernels at offsets that are
not zero.

Move ubldr text section to the start of the output file, so that when you
create a stripped .bin file from it the entry point is the first byte of
the file. (Will allow "load $addr $file ; go $addr" in u-boot.)

Create a relocatable instance of ubldr for ARM (ubldr.bin).

Re-link ubldr when any of its libraries change.

An ARM kernel can be loaded at any 2MB boundary, make ubldr aware of that.

MFC r274407

Fix incorrect reading of 32-bit modinfo by 64-bit loaders.

The various structures in the mod_metadata set of a FreeBSD kernel and
modules contain pointers. The FreeBSD loader correctly deals with a
mismatch in loader and kernel pointer size (e.g. 32-bit i386/ppc
loader, loading 64-bit amd64/ppc64 kernels), but wasn't dealing with
the inverse case where a 64-bit loader was loading a 32-bit kernel.

MFC r277962, r277988, r282661, r282727, r282731, r283013, r283035:

Add support for booting relocatable kernels on PowerPC.

Add code to support loading relocatable kernels at offsets that are
not zero.

Move ubldr text section to the start of the output file, so that when you
create a stripped .bin file from it the entry point is the first byte of
the file. (Will allow "load $addr $file ; go $addr" in u-boot.)

Create a relocatable instance of ubldr for ARM (ubldr.bin).

Re-link ubldr when any of its libraries change.

An ARM kernel can be loaded at any 2MB boundary, make ubldr aware of that.

MFC r274407

Fix incorrect reading of 32-bit modinfo by 64-bit loaders.

The various structures in the mod_metadata set of a FreeBSD kernel and
modules contain pointers. The FreeBSD loader correctly deals with a
mismatch in loader and kernel pointer size (e.g. 32-bit i386/ppc
loader, loading 64-bit amd64/ppc64 kernels), but wasn't dealing with
the inverse case where a 64-bit loader was loading a 32-bit kernel.