sh: IPR/INTC2 IRQ setup consolidation.

This patch unifies the cpu specific interrupt setup functions for
interrupt controller blocks such as ipr, intc2 and intc. There is no
point in having separate functions for each interrupt controller, so
let's clean this up.

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