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

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

Don't build the ski loader anymore. The code is not deleted just yet,
as it explains the distinction between the common and the platform-
specific code.

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.

Hookup the efi subdirectory.

Unhook libski and skiload and hook up ski.

Add a version of the loader which runs under SKI, the HP ia64 simulator.
This loader is quite functional and can load and run kernels. The kernels
don't quite work right after loading but that should be easily fixable.

Add "empty" makefile. Cross-building fails without it.