mISDN: Order IPAC register defines

It looks like IPAC/ISAC chips register defines weren't in any particular
order.

Order them by their number to make it easier to spot holes.

Signed-off-by: Maciej S. Szmigiero <mail@maciej.szmigiero.name>
Acked-by: Karsten Keil <keil@b1-systems.de>
Signed-off-by: David S. Miller <davem@davemloft.net>