CSS: Implement topology support for System power domain

This patch implements the necessary topology changes for supporting
system power domain on CSS platforms. The definition of PLAT_MAX_PWR_LVL and
PLAT_NUM_PWR_DOMAINS macros are removed from arm_def.h and are made platform
specific. In addition, the `arm_power_domain_tree_desc[]` and
`arm_pm_idle_states[]` are modified to support the system power domain
at level 2. With this patch, even though the power management operations
involving the system power domain will not return any error, the platform
layer will silently ignore any operations to the power domain. The actual
power management support for the system power domain will be added later.

Change-Id: I791867eded5156754fe898f9cdc6bba361e5a379
diff --git a/plat/arm/board/juno/include/platform_def.h b/plat/arm/board/juno/include/platform_def.h
index ba93254..39283c5 100644
--- a/plat/arm/board/juno/include/platform_def.h
+++ b/plat/arm/board/juno/include/platform_def.h
@@ -41,9 +41,13 @@
 #include <v2m_def.h>
 #include "../juno_def.h"
 
-
+/* Juno supports system power domain */
+#define PLAT_MAX_PWR_LVL		ARM_PWR_LVL2
+#define PLAT_NUM_PWR_DOMAINS		(ARM_SYSTEM_COUNT + \
+					ARM_CLUSTER_COUNT + \
+					PLATFORM_CORE_COUNT)
 /*
- * Most platform porting definitions provided by included headers
+ * Other platform porting definitions are provided by included headers
  */
 
 /*