sparc32: drop sun4c support

sparc32: drop sun4c support

Machines with sun4c support are very rare these days, and noone
is using them for any practical purposes.
The sun4c support has been know broken for quite some time too.

So rather than trying to keep it up-to-date, lets get rid of it.
This allows us to do some very welcome cleanup of sparc32 support.

Updated the former sun4c specifc nmi (which was also used
for sun4m UP) to be a generic UP NMI.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: David S. Miller <davem@davemloft.net>