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/armv8/Makefile b/arch/arm/cpu/armv8/Makefile
index 65915ee..c447085 100644
--- a/arch/arm/cpu/armv8/Makefile
+++ b/arch/arm/cpu/armv8/Makefile
@@ -16,6 +16,8 @@
 obj-y	+= transition.o
 obj-y	+= fwcall.o
 obj-y	+= cpu-dt.o
+obj-$(CONFIG_ARM_SMCCC)		+= smccc-call.o
+
 ifndef CONFIG_SPL_BUILD
 obj-$(CONFIG_ARMV8_SPIN_TABLE) += spin_table.o spin_table_v8.o
 endif