sh: rework ipr code

sh: rework ipr code

This patch reworks the ipr code by grouping the offset array together
with the ipr_data structure in a new data structure called ipr_desc.
This new structure also contains the name of the controller in struct
irq_chip. The idea behind putting struct irq_chip in there is that we
can use offsetof() to locate the base addresses in the irq_chip
callbacks. This strategy has much in common with the recently merged
intc2 code.

One logic change has been made - the original ipr code enabled the
interrupts by default but with this patch they are all disabled by
default.

Signed-off-by: Magnus Damm <damm@igel.co.jp>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>