m32r: enable arbitary speed tty rate setting

Add the defines and constants needed for the M32R platform to support the
arbitary speed tty ioctls.

Signed-off-by: Alan Cox <alan@redhat.com>
Cc: Hirokazu Takata <takata@linux-m32r.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>