[ARM] 3224/1: add masked thread interrupt status registers for ixp2000

Patch from Lennert Buytenhek

In its interrupt handler, the (NAPI) ixp2000 netdev driver needs to use
the masked thread interrupt status register (instead of the raw one) to
prevent scheduling polling when polling is already running when a TXdone
interrupt comes in.  The definitions for the masked status registers were
not in yet, so this patch adds them.

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