Introduce utils.h header file

This patch introduces a new header file: include/lib/utils.h.
Its purpose is to provide generic macros and helper functions that
are independent of any BL image, architecture, platform and even
not specific to Trusted Firmware.

For now, it contains only 2 macros: ARRAY_SIZE() and
IS_POWER_OF_TWO(). These were previously defined in bl_common.h and
xlat_tables.c respectively.

bl_common.h includes utils.h to retain compatibility for platforms
that relied on bl_common.h for the ARRAY_SIZE() macro. Upstream
platform ports that use this macro have been updated to include
utils.h.

Change-Id: I960450f54134f25d1710bfbdc4184f12c049a9a9
diff --git a/plat/arm/common/arm_io_storage.c b/plat/arm/common/arm_io_storage.c
index 153fdfe..42435a7 100644
--- a/plat/arm/common/arm_io_storage.c
+++ b/plat/arm/common/arm_io_storage.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2015, ARM Limited and Contributors. All rights reserved.
+ * Copyright (c) 2015-2016, ARM Limited and Contributors. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are met:
@@ -28,7 +28,6 @@
  * POSSIBILITY OF SUCH DAMAGE.
  */
 #include <assert.h>
-#include <bl_common.h>		/* For ARRAY_SIZE */
 #include <debug.h>
 #include <firmware_image_package.h>
 #include <io_driver.h>
@@ -37,6 +36,7 @@
 #include <io_storage.h>
 #include <platform_def.h>
 #include <string.h>
+#include <utils.h>
 
 /* IO devices */
 static const io_dev_connector_t *fip_dev_con;