ARM: use common irqchip_init for GIC init

From: Rob Herring <rob.herring at calxeda.com>

Convert all GIC DT initialization over to use common irqchip_init
function.

Signed-off-by: Rob Herring <rob.herring at calxeda.com>
Cc: Russell King <linux at arm.linux.org.uk>
Cc: Kukjin Kim <kgene.kim at samsung.com>
Cc: Shawn Guo <shawn.guo at linaro.org>
Cc: Sascha Hauer <kernel at pengutronix.de>
Cc: David Brown <davidb at codeaurora.org>
Cc: Daniel Walker <dwalker at fifo99.com>
Cc: Bryan Huntsman <bryanh at codeaurora.org>
Cc: Tony Lindgren <tony at atomide.com>
Cc: Paul Mundt <lethal at linux-sh.org>
Cc: Magnus Damm <magnus.damm at gmail.com>
Cc: Dinh Nguyen <dinguyen at altera.com>
Cc: Viresh Kumar <viresh.linux at gmail.com>
Cc: Shiraz Hashim <shiraz.hashim at st.com>
Cc: Stephen Warren <swarren at wwwdotorg.org>
Cc: Srinidhi Kasagar <srinidhi.kasagar at stericsson.com>
Cc: Linus Walleij <linus.walleij at linaro.org>