Move PSCI to runtime services directory

This patch creates a 'services' directory and moves the PSCI under
it. Other runtime services e.g. the Secure Payload Dispatcher service
will be placed under the same directory in the future.

Also fixes issue ARM-software/tf-issues#12

Change-Id: I187f83dcb660b728f82155d91882e961d2255068
diff --git a/bl31/bl31.mk b/bl31/bl31.mk
index fec8ebe..1522b83 100644
--- a/bl31/bl31.mk
+++ b/bl31/bl31.mk
@@ -33,13 +33,13 @@
 				arch/system/gic				\
 				plat/${PLAT}				\
 				arch/${ARCH}				\
-				common/psci				\
+				services/psci				\
 				lib/sync/locks/bakery			\
 				plat/${PLAT}/${ARCH}			\
 				${PLAT_BL31_C_VPATH}
 
 vpath			%.S	lib/arch/${ARCH}			\
-				common/psci				\
+				services/psci				\
 				include					\
 				plat/${PLAT}/${ARCH}			\
 				lib/sync/locks/exclusive		\