Move spinlock library code to AArch64 folder

This patch moves the assembly exclusive lock library code
`spinlock.S` into architecture specific folder `aarch64`.
A stub file which includes the file from new location is
retained at the original location for compatibility. The BL
makefiles are also modified to include the file from the new
location.

Change-Id: Ide0b601b79c439e390c3a017d93220a66be73543
diff --git a/bl32/tsp/tsp.mk b/bl32/tsp/tsp.mk
index a502428..2f3391e 100644
--- a/bl32/tsp/tsp.mk
+++ b/bl32/tsp/tsp.mk
@@ -37,7 +37,7 @@
 				bl32/tsp/tsp_interrupt.c		\
 				bl32/tsp/tsp_timer.c			\
 				common/aarch64/early_exceptions.S	\
-				lib/locks/exclusive/spinlock.S
+				lib/locks/exclusive/aarch64/spinlock.S
 
 BL32_LINKERFILE		:=	bl32/tsp/tsp.ld.S