gpio: aspeed: port Linux dt-bindings header file

Makes it easier to add readable GPIO definitions in DTS files
for Aspeed SOC based boards.

Ported with small edits to add IBM copyright statement and fix
for checkpatch warning.

Signed-off-by: Dhananjay Phadke <dphadke@linux.microsoft.com>
Reviewed-by: Billy Tsai <billy_tsai@aspeedtech.com>
Acked-by: Chia-Wei Wang <chiawei_wang@aspeedtech.com>

include/dt-bindings/gpio/aspeed-gpio.h

@@ -0,0 +1,51 @@
+/* SPDX-License-Identifier: GPL-2.0+ */
+/*
+ * Copyright 2022 IBM Corp.
+ *
+ * This header provides constants for binding aspeed,*-gpio.
+ *
+ * The first cell in Aspeed's GPIO specifier is the GPIO ID. The macros below
+ * provide names for this.
+ *
+ * The second cell contains standard flag values specified in gpio.h.
+ */
+
+#ifndef _DT_BINDINGS_GPIO_ASPEED_GPIO_H
+#define _DT_BINDINGS_GPIO_ASPEED_GPIO_H
+
+#include <dt-bindings/gpio/gpio.h>
+
+#define ASPEED_GPIO_PORT_A 0
+#define ASPEED_GPIO_PORT_B 1
+#define ASPEED_GPIO_PORT_C 2
+#define ASPEED_GPIO_PORT_D 3
+#define ASPEED_GPIO_PORT_E 4
+#define ASPEED_GPIO_PORT_F 5
+#define ASPEED_GPIO_PORT_G 6
+#define ASPEED_GPIO_PORT_H 7
+#define ASPEED_GPIO_PORT_I 8
+#define ASPEED_GPIO_PORT_J 9
+#define ASPEED_GPIO_PORT_K 10
+#define ASPEED_GPIO_PORT_L 11
+#define ASPEED_GPIO_PORT_M 12
+#define ASPEED_GPIO_PORT_N 13
+#define ASPEED_GPIO_PORT_O 14
+#define ASPEED_GPIO_PORT_P 15
+#define ASPEED_GPIO_PORT_Q 16
+#define ASPEED_GPIO_PORT_R 17
+#define ASPEED_GPIO_PORT_S 18
+#define ASPEED_GPIO_PORT_T 19
+#define ASPEED_GPIO_PORT_U 20
+#define ASPEED_GPIO_PORT_V 21
+#define ASPEED_GPIO_PORT_W 22
+#define ASPEED_GPIO_PORT_X 23
+#define ASPEED_GPIO_PORT_Y 24
+#define ASPEED_GPIO_PORT_Z 25
+#define ASPEED_GPIO_PORT_AA 26
+#define ASPEED_GPIO_PORT_AB 27
+#define ASPEED_GPIO_PORT_AC 28
+
+#define ASPEED_GPIO(port, offset) \
+	((ASPEED_GPIO_PORT_##port * 8) + (offset))
+
+#endif