[PARISC] [MUX] Detect multiple cards in the correct order

This patch follows the example of the 8250_gsc
driver by probing for specific built-in Mux
cards first.  This allows the system to preserve
the correct detection order with multiple Mux
cards.

Signed-off-by: Ryan Bradetich <rbrad@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>