irqchip: Add driver for Loongson-1 intc v6
From: Jiaxun Yang
Date: Fri Feb 01 2019 - 01:22:57 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.
v5->v6: Fix doc and collect Rob's review tag.