[IA64] Fix serial console on Tiger2 & Tiger4

[IA64] Fix serial console on Tiger2 & Tiger4

I inadvertently broke the serial console on Intel Tiger systems by
assuming they were registering a com1 at 0x3f8.  Instead, unconditionally
register both com ports (the ns16550 driver will throw away any that
don't have baud == 0) and create a function to detect the Tiger systems.
This should setup reasonable default com port values, but they can still
be superceded using com1= and com2= boot time parameters.

Signed-off-by: Alex Williamson <alex.williamson@hp.com>