[ARM] 3379/1: ixp2000: use generic 8250 debug macros

Patch from Lennert Buytenhek

The xscale UART in the ixp2000 is basically just an 8250 UART (with
some extra bits and pieces), so we can use the generic 8250 debug
macros on the ixp2000.

Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>