[POWERPC] 83xx: Return a point to the struct ipic from ipic_init()

It's useful to have access to struct ipic handle that just got created
in ipic_init().

For example, if we want to setup an external IRQ with out
a device node we need access ipic->irqhost to create the virtual to HW
IRQ mapping and to set the IRQ sense.  With this we can mimic the old
sense array concept that existed in arch/ppc.

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>