[POWERPC] Enable arbitary speed tty ioctls and split input/output speed

Adding the defines/macros activates the existing code in the tty layer and
allows this platform to use the arbitary speed ioctl setting layer

Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>