We don't enable the BTB on the ixp2350 as that can cause weird
crashes (erratum #42.)  However, some bootloaders enable the BTB,
which means that we have to disable the BTB explicitly.

Found thanks to Tom Rini.
Signed-off-by: Lennert Buytenhek <buytenh@wantstofly.org>
Signed-off-by: Deepak Saxena <dsaxena@plexity.net>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>