Include `plat_psci_common.c` from the new location

The `plat_psci_common.c` was moved to the new location `plat/common`
and a stub file was retained at previous location for compatibility. This
patch modifies the platform makefiles to include the file from the new
location.

Change-Id: Iabddeeb824e9a5d72d176d7c644735966c8c0699
diff --git a/plat/rockchip/rk3368/platform.mk b/plat/rockchip/rk3368/platform.mk
index 50eda32..c9ec564 100644
--- a/plat/rockchip/rk3368/platform.mk
+++ b/plat/rockchip/rk3368/platform.mk
@@ -51,7 +51,7 @@
 PLAT_BL_COMMON_SOURCES	:=	lib/xlat_tables/xlat_tables_common.c		\
 				lib/xlat_tables/aarch64/xlat_tables.c		\
 				plat/common/aarch64/plat_common.c		\
-				plat/common/aarch64/plat_psci_common.c
+				plat/common/plat_psci_common.c
 
 BL31_SOURCES		+=	${RK_GIC_SOURCES}				\
 				drivers/arm/cci/cci.c				\