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/arch/arm/cpu/armv7/smccc-call.S b/arch/arm/cpu/armv7/smccc-call.S
index e5d4306..c2fdbad 100644
--- a/arch/arm/cpu/armv7/smccc-call.S
+++ b/arch/arm/cpu/armv7/smccc-call.S
@@ -1,22 +1,14 @@
 /*
  * 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
  */
 #include <linux/linkage.h>
 
 #include <asm/opcodes-sec.h>
 #include <asm/opcodes-virt.h>
-#include <asm/unwind.h>
 
+#define UNWIND(x...)
 	/*
 	 * Wrap c macros in asm macros to delay expansion until after the
 	 * SMCCC asm macro is expanded.