[POWERPC] CPM_UART: Fix non-console transmit

The SMC and SCC hardware transmitter is enabled at the wrong
place. Simply writing twice to the non-console port, like

$ echo asdf > /dev/ttyCPM1
$ echo asdf > /dev/ttyCPM1

puts the shell into endless uninterruptible sleep, since the
transmitter is stopped after the first write, and is not enabled
before the shutdown function of the second write. Thus the transmit
buffers are never emptied.

Signed-off-by: Kalle Pokki <kalle.pokki@iki.fi>
Signed-off-by: Vitaly Bordug <vbordug@ru.mvista.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>