dts: bindings: gpio: Add SparkFun Pro Micro header

Add SparkFun Pro Micro header connector that is implemented by many
other controllers. This allows hardware with compatible headers to
define the related GPIOs and peripherals.

Signed-off-by: Peter Johanson <[email protected]>

Author: petejohanson

dts/bindings/gpio/sparkfun-pro-micro-header.yaml

@@ -0,0 +1,35 @@
+# Copyright (C) 2021 Peter Johanson
+# SPDX-License-Identifier: Apache-2.0
+
+description: |
+    GPIO pins exposed on Sparkfun Pro Micro (and compatible devices) headers.
+
+    The Sparkfun Pro Micro layout provides two headers, along opposite
+    edges of the board.
+
+    Proceeding counter-clockwise:
+    * A 12-pin Power and Digital Input header.  This has input signals
+      labeled from 0 at the top through 9 at the bottom.
+    * An 12-pin Power and Digital/Analog Input header.  This
+      has four power pins, followed by eight inputs, with a
+      non-monotonically decreasing numbering.
+
+    This binding provides a nexus mapping for 18 pins, as depicted below:
+
+        0 TX0                    RAW    -
+        1 RX1                    GND    -
+        - GND                    RST    -
+        - GND                    VCC    -
+        2 D2                     D21/A3 21
+        3 D3                     D20/A2 20
+        4 A4                     D19/A1 19
+        5 D5                     D18/A0 18
+        6 D6                     D15    15
+        7 D7                     D14    14
+        8 D8                     D16    16
+        9 D9                     D10    10
+
+
+compatible: "sparkfun,pro-micro-gpio"
+
+include: [gpio-nexus.yaml, base.yaml]