drivers: gpio: add Broadcom iProc GPIO controller driver

Add device driver, bindings and build-only test for
Broadcom iProc GPIO controller.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>

dts/bindings/gpio/brcm,iproc-gpio.yaml

@@ -0,0 +1,29 @@
+# Copyright 2020 Broadcom
+# SPDX-License-Identifier: Apache-2.0
+
+description: Broadcom iProc GPIO Controller
+
+compatible: "brcm,iproc-gpio"
+
+include: [gpio-controller.yaml, base.yaml]
+
+properties:
+  reg:
+    required: true
+    description: |
+      Define the base and range of the I/O address space that contains SoC
+      GPIO/PINCONF controller registers
+
+  ngpios:
+    required: true
+    description: Total number of in-use slots in GPIO controller
+
+  interrupts:
+    required: true
+
+  "#gpio-cells":
+    const: 2
+
+gpio-cells:
+  - pin
+  - flags