tty: i386/x86_64 arbitary speed support

Adds the needed TCGETS2/TCSETS2 ioctl calls, structures, defines and the like.
Tested against the test suite and passes.  Other platforms should need
roughly the same change.

Signed-off-by: Alan Cox <alan@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>