ARM: adjust arm-smccc code for use in U-Boot

Adjust ARM SMC Calling Convention code for U-Boot:
  - Replace the license block with SPDX
  - Change path to asm-offsets.h
  - Define UNWIND() as no-op
  - Add Kconfig entry
  - Add asm-offsets

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/include/linux/arm-smccc.h b/include/linux/arm-smccc.h
index 4c5bca3..28e61ce 100644
--- a/include/linux/arm-smccc.h
+++ b/include/linux/arm-smccc.h
@@ -1,15 +1,7 @@
 /*
  * Copyright (c) 2015, Linaro Limited
  *
- * This software is licensed under the terms of the GNU General Public
- * License version 2, as published by the Free Software Foundation, and
- * may be copied, distributed, and modified under those terms.
- *
- * This program is distributed in the hope that it will be useful,
- * but WITHOUT ANY WARRANTY; without even the implied warranty of
- * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
- * GNU General Public License for more details.
- *
+ * SPDX-License-Identifier:	GPL-2.0
  */
 #ifndef __LINUX_ARM_SMCCC_H
 #define __LINUX_ARM_SMCCC_H