input: convert kscan_mchp_xec.c driver to input

Convert the XEC keyboard scanning driver from kscan to input, add the
corresponding kscan compatibility node to the current board, build test
only.

Signed-off-by: Fabio Baltieri <fabiobaltieri@google.com>

dts/bindings/kscan/microchip,xec-kscan.yaml

@@ -1,32 +0,0 @@
-# Copyright (c) 2019, Intel Corporation
-# Copyright (c) 2021, Microchip Technology Inc.
-# SPDX-License-Identifier: Apache-2.0
-
-description: Microchip XEC keyboard matrix controller
-
-compatible: "microchip,xec-kscan"
-
-include: [kscan.yaml, pinctrl-device.yaml]
-
-properties:
-  "#address-cells":
-    required: true
-    const: 1
-  "#size-cells":
-    type: int
-    const: 0
-  reg:
-    required: true
-
-  interrupts:
-    required: true
-
-  girqs:
-    type: array
-    required: true
-    description: Array of pairs of GIRQ number and bit position
-
-  pcrs:
-    type: array
-    required: true
-    description: ADC PCR register index and bit position