drivers/spi/ice40: migrate to SPDX identifier

Most tools used for compliance and SBOM generation use SPDX identifiers
This change brings us a step closer to an easy SBOM generation.

Copyright and Author information is missing from the License and was filled with
commit authorship
    Signed-off-by: Jakub Janousek <[email protected]>

Signed-off-by: Alin Jerpelea <[email protected]>

Author: jerpelea

drivers/spi/ice40.c

@@ -1,6 +1,10 @@
 /****************************************************************************
  * drivers/spi/ice40.c
  *
+ * SPDX-License-Identifier: Apache-2.0
+ * SPDX-FileCopyrightText: Jakub Janousek <[email protected]>
+ * SPDX-FileContributor: Jakub Janousek <[email protected]>
+ *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at