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/aarch64/bl1_entrypoint.S b/bl1/aarch64/bl1_entrypoint.S
index e7f92c7..82330c1 100644
--- a/bl1/aarch64/bl1_entrypoint.S
+++ b/bl1/aarch64/bl1_entrypoint.S
@@ -57,7 +57,7 @@
 	 * reset e.g. cache, tlb invalidations etc.
 	 * ---------------------------------------------
 	 */
-	bl	cpu_reset_handler
+	bl	reset_handler
 
 	/* ---------------------------------------------
 	 * Enable the instruction cache, stack pointer