Introduce framework for CPU specific operations

This patch introduces a framework which will allow CPUs to perform
implementation defined actions after a CPU reset, during a CPU or cluster power
down, and when a crash occurs. CPU specific reset handlers have been implemented
in this patch. Other handlers will be implemented in subsequent patches.

Also moved cpu_helpers.S to the new directory lib/cpus/aarch64/.

Change-Id: I1ca1bade4d101d11a898fb30fea2669f9b37b956
diff --git a/bl1/bl1.mk b/bl1/bl1.mk
index 032dc5e..8e73bef 100644
--- a/bl1/bl1.mk
+++ b/bl1/bl1.mk
@@ -32,6 +32,6 @@
 				bl1/aarch64/bl1_arch_setup.c		\
 				bl1/aarch64/bl1_entrypoint.S		\
 				bl1/aarch64/bl1_exceptions.S		\
-				lib/aarch64/cpu_helpers.S
+				lib/cpus/aarch64/cpu_helpers.S
 
 BL1_LINKERFILE		:=	bl1/bl1.ld.S