entry.S access percpu + global data defined in
sun4m_irq.c - so move the types to irq.h.
This makes sparse happy and allow us to utilize
asm-offsets later.

Also updated a few comments in the sun4m_irq.c file.
Signed-off-by: NSam Ravnborg <sam@ravnborg.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>