add bi-endian support to the libsa ufs reader and enable it in efiboot.

ffs frontends to "ufs.c" now also define ufs_dinode_swap, ufs_indp_swap,
and FS_MAGIC (moved from ufs.c #if segments.)  these are used to call
the right (32/64 bit) ffsv1/v2 version.

ufs.c 'struct file' gains f_swapped member.  accessors for d_magic,
d_reclen, and d_ino are introduced (they need to be swapped.)  sfter
reading an inode from disk, read_inode() may call ufs_dinode_swap().
indirect block number and caches may be swapped.

error handling in ffs_find_superblock() is cleaned up.  (size is slightly
reduced on some ports with this part.)

defaults for new defines added to ufs.c.  (XXX: we build ufs.c but i think
all the consumers don't use it, and we can stop building it.)

LFS support is not included.

add a cut-down copy of ffs_bswap.c from the kernel.

also enable bi-endian disklabel support in efiboot.

most ports build and sizes compared for platforms that don't enable this
code and all but one saw reduced code size.  booted several platforms with
new boot code.

(mrg)