sparc: remove CONFIG_SUN4

While doing some easy cleanups on the sparc code I noticed that the
CONFIG_SUN4 code seems to be worse than the rest - there were some
"I don't know how it should work, but the current code definitely cannot
work." places.

And while I have seen people running Linux on machines like a
SPARCstation 5 a few years ago I don't recall having seen sun4
machines, even less ones running Linux.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>