MIPS: BMIPS: Delete the irqchip driver from irq.c

MIPS: BMIPS: Delete the irqchip driver from irq.c

BCM3384/BCM63xx can use the common drivers/irqchip/irq-bcm7120-l2.c for
this purpose; BCM7xxx will use drivers/irqchip/irq-bcm7038-l1.c.  We no
longer need this code under arch/mips.

[ralf@linux-mips.org: Fix conflicts.]

Signed-off-by: Kevin Cernekee <cernekee@gmail.com>
Cc: f.fainelli@gmail.com
Cc: jaedon.shin@gmail.com
Cc: abrestic@chromium.org
Cc: tglx@linutronix.de
Cc: jason@lakedaemon.net
Cc: jogo@openwrt.org
Cc: arnd@arndb.de
Cc: computersforpeace@gmail.com
Cc: linux-mips@linux-mips.org
Cc: devicetree@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Patchwork: https://patchwork.linux-mips.org/patch/8853/
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>