sparc32,sun4c: irq file cleanup

- drop filename in header
- drop unused includes
- add description of sun4c interrupts (from davem)
- add spaces after reserved words

This is partly based on a patch from: David Miller <davem@davemloft.net>

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