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/Makefile b/arch/arm/cpu/armv7/Makefile
index 02e8778..3a9913a 100644
--- a/arch/arm/cpu/armv7/Makefile
+++ b/arch/arm/cpu/armv7/Makefile
@@ -18,6 +18,7 @@
 endif
 endif
 
+obj-$(CONFIG_ARM_SMCCC)		+= smccc-call.o
 obj-$(CONFIG_ARMV7_NONSEC)	+= nonsec_virt.o virt-v7.o virt-dt.o
 obj-$(CONFIG_ARMV7_PSCI)	+= psci.o psci-common.o