irqchip: Add driver for Loongson-1 intc v5
From: Jiaxun Yang
Date: Mon Jan 28 2019 - 22:05:16 EST
v1->v2: Fix SPDX-License-Identifier
v2->v3: Rework according suggestions from Marc Zyngier, Thanks.
v3->v4: Rework the driver into a single chip driver.
v4->v5: Fix minor issues.