serial: fix parisc boot hang

This is a partial revert of 2f2dafe7 (serial: serial_core.c: printk
replacement) which gets us booting again.  The real problem seems to be
the _emit path in early boot.  However, until we can root cause it, we
need at least to get boot working.

Fixes: 2f2dafe7
Cc: stable@vger.kernel.org
Signed-off-by: James Bottomley <JBottomley@Parallels.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>