hwspinlock/core: Switch to SPDX license identifier

Use the appropriate SPDX license identifier in the Hwspinlock core
driver source files and drop the previous boilerplate license text.

Signed-off-by: Suman Anna <s-anna@ti.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/hwspinlock/Kconfig

@@ -1,3 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0
 #
 # Generic HWSPINLOCK framework
 #