Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

o Bump the EFI loader version to 3.1.
o Add the about, pbvm and reboot commands.
o Trim the banner (suppress maker and date).

Turn PBVM page table entries into PTEs so that they can be inserted
into the TLB as-is.

While here, have ia64_platform_alloc() return ~0UL on failure.

MFaltix:
Add support for Pre-Boot Virtual Memory (PBVM) to the loader.

PBVM allows us to link the kernel at a fixed virtual address without
having to make any assumptions about the physical memory layout. On
the SGI Altix 350 for example, there's no usuable physical memory
below 192GB. Also, the PBVM allows us to control better where we're
going to physically load the kernel and its modules so that we can
make sure we load the kernel in memory that's close to the BSP.

The PBVM is managed by a simple page table. The minimum size of the
page table is 4KB (EFI page size) and the maximum is currently set
to 1MB. A page in the PBVM is 64KB, as that's the maximum alignment
one can specify in a linker script. The bottom line is that PBVM is
between 64KB and 8GB in size.

The loader maps the PBVM page table at a fixed virtual address and
using a single translations. The PBVM itself is also mapped using a
single translation for a maximum of 32MB.

While here, increase the heap in the EFI loader from 512KB to 2MB
and set the stage for supporting relocatable modules.

Major rework of the ia64 loaders. The two primary objectives are:
1. Make libefi portable by removing ia64 specific code and build
it on i386 and amd64 by default to prevent regressions. These
changes include fixes and improvements over previous code to
establish or improve APIs where none existed or when the amount
of kluging was unacceptably high.
2. Increase the amount of sharing between the efi and ski loaders
to improve maintainability of the loaders and simplify making
changes to the loader-kernel handshaking in the future.

The version of the efi and ski loaders are now both changed to 1.2
as user visible improvements and changes have been made.

Start each of the license/copyright comments with /*-

Add efimd.c. This file contains MD code used by the EFI library. While
changing the Makefile, fail the creation of loader.efi when there are
unresolved symbols in loader.sym. This avoids silently creating a
faulty EFI binary.