sh: rework intc2 code

The shared intc2 code currently contains cpu-specific #ifdefs.
This is a tad unclean and it prevents us from using the shared code
to drive board-specific irqs on the se7780 board.

This patch reworks the intc2 code by moving the base addresses of
the intc2 registers into struct intc2_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.

One logic change has been made - the original shared intc2 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>