parisc: Autodetect default output device and set console= kernel parameter

Usually palo (the PA-RISC boot loader) will check at boot time if the
machine/firmware was configured to use the serial line (ttyS0, SERIAL_x)
or the graphical display (tty0, graph) as default output device and add
the correct "console=ttyS0" or "console=tty0" Linux kernel parameter to
the kernel command line when starting the Linux kernel.

But the kernel could also have been started via the HP-UX boot loader
or directly in qemu, in which cases the console parameter is missing.

This patch fixes this problem by adding the correct console= parameter
if it's missing in the current kernel command line.

Signed-off-by: Helge Deller <deller@gmx.de>