sh: intc - add support for x3

This patch converts the cpu specific interrupt setup code for x3 from
intc2 to intc. New vectors are also added to match the preliminary
information.

Use plat_irq_setup_pins() to select between IRQ and IRL mode for IRQ0-3.

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