alpha: remove DECpc AXP150 (Jensen) support

This is one of the hackiest Alpha machines, and the only one without
PCI support. Removing this allows cleaning up code in eise and tty
drivers in addition to the architecture code.

Acked-by: Paul E. McKenney <paulmck@kernel.org>
Acked-by: Matt Turner <mattst88@gmail.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>