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/include/asm/opcodes.h b/arch/arm/include/asm/opcodes.h
index e796c59..199f0ba 100644
--- a/arch/arm/include/asm/opcodes.h
+++ b/arch/arm/include/asm/opcodes.h
@@ -1,9 +1,7 @@
 /*
  *  arch/arm/include/asm/opcodes.h
  *
- * This program is free software; you can redistribute it and/or modify
- * it under the terms of the GNU General Public License version 2 as
- * published by the Free Software Foundation.
+ * SPDX-License-Identifier:	GPL-2.0
  */
 
 #ifndef __ASM_ARM_OPCODES_H