dts: bindings: slave: Add yaml file to support spi flash

add yaml file to support spi flash

Signed-off-by: Savinay Dharmappa <savinay.dharmappa@intel.com>

dts/bindings/slave/spi,flash.yaml

@@ -0,0 +1,25 @@
+#
+# Copyright (c) 2018, Intel Corporation
+#
+# SPDX-License-Identifier: Apache-2.0
+#
+---
+title: SPI NOR FLASH
+version: 0.1
+
+description: >
+    This binding gives a base representation of SPI slave NOR FLASH
+
+inherits:
+    !include spi-device.yaml
+
+properties:
+    compatible:
+      constraint: "spi,flash"
+    size:
+      type: int
+      category: required
+      description: SPI Slave NOR FLASH Size in KiB
+      generation: define
+
+...