sparc32,sun4m: percpu and global register definitions moved to irq.h

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