ARM: 8280/1: sa1100: switch to irq_domain_add_simple()

As now both SC and GPIO irq domains start from 0 hwirq and do not
contain holes, switch to using irq_domain_add_simple() instead of
irq_domain_add_legacy().

Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Tested-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>