ARM: OMAP2+: drop unused function

gic_init_irq() is no longer used as of:

    commit b42b9181
    Author: Tony Lindgren <tony@atomide.com>
    Date:   Thu May 30 12:53:05 2013 -0700

        ARM: OMAP2+: Remove board-omap4panda.c

Drop it.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Cc: Tony Lindgren <tony@atomide.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-omap@vger.kernel.org
Signed-off-by: Tony Lindgren <tony@atomide.com>