irqchip: mips-gic: Remove gic_init()

All in-tree platforms now probe the GIC driver using device tree, and as
such nothing calls gic_init() any longer. Remove the dead code.

Signed-off-by: Paul Burton <paul.burton@imgtec.com>
Acked-by: Marc Zyngier <marc.zyngier@arm.com>
Cc: Jason Cooper <jason@lakedaemon.net>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/17043/


Signed-off-by: Ralf Baechle <ralf@linux-mips.org>