hv: add SPDX license id to Kconfig

Missing license on Kconfig file.

Signed-off-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: K. Y. Srinivasan <kys@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/hv/Kconfig

@@ -1,3 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+
 menu "Microsoft Hyper-V guest support"
 
 config HYPERV