move timer #defines & remove duplicate declaration

This patch removes the duplicate declaration of psci_cpu_on in psci.h
and moves the constants for the system level implementation of the
generic timer from arch_helpers.h to arch.h. All other architectural
constants are defined in arch.h so there is no need to add them to
arch_helpers.h

Change-Id: Ia8ad3f91854f7e57fce31873773eede55c384ff1
diff --git a/include/aarch64/arch.h b/include/aarch64/arch.h
index 143dc6c..4548926 100644
--- a/include/aarch64/arch.h
+++ b/include/aarch64/arch.h
@@ -71,6 +71,16 @@
 #define CPUECTLR_EL1	S3_1_C15_C2_1
 
 /*******************************************************************************
+ * Generic timer memory mapped registers & offsets
+ ******************************************************************************/
+#define CNTCR_OFF			0x000
+#define CNTFID_OFF			0x020
+
+#define CNTCR_EN			(1 << 0)
+#define CNTCR_HDBG			(1 << 1)
+#define CNTCR_FCREQ(x)			(1 << (8 + (x)))
+
+/*******************************************************************************
  * System register bit definitions
  ******************************************************************************/
 /* CLIDR definitions */