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/Makefile b/Makefile
index 4d925b3..a5a3a78 100644
--- a/Makefile
+++ b/Makefile
@@ -131,7 +131,7 @@
 				-Iinclude/${ARCH}/		\
 				-Iinclude/			\
 				-Iarch/system/gic		\
-				-Icommon/psci			\
+				-Iservices/psci			\
 				-Iinclude/stdlib		\
 				-Iinclude/stdlib/sys		\
 				-Iplat/${PLAT}			\