Remove file system support based on the simple file system protocol

as this only allows us to access file systems that EFI knows about.
With a loader that can only use EFI-supported file systems, we're
forced to put /boot on the EFI system partition. This is suboptimal
in the following ways:
1.  With /boot a symlink to /efi/boot, mergemaster complains about
    the mismatch and there's no quick solution.
2.  The EFI loader can only boot a single version of FreeBSD. There's
    no way to install multiple versions of FreeBSD and select one
    at the loader prompt.
3.  ZFS maintains /boot/zfs/zpool.cache and with /boot a symlink we
    end up with the file on a MSDOS file system. ZFS does not have
    proper handling of file systems that are under Giant.

Implement a disk device based on the block I/O protocol instead and
pull in file system code from libstand. The disk devices are really
the partitions that EFI knows about.

This change is backward compatible.

MFC after:	1 week

0 files changed, 0 insertions, 0 deletions