rockchip: rk3399: add stopwatch functions to m0

There is system timer in m0, we can use it to implement a set of
stopwatch functions for measuring timeouts.

Signed-off-by: Lin Huang <hl@rock-chips.com>
Signed-off-by: Derek Basehore <dbasehore@chromium.org>
diff --git a/plat/rockchip/rk3399/drivers/m0/Makefile b/plat/rockchip/rk3399/drivers/m0/Makefile
index ec2b3d2..2d07d24 100644
--- a/plat/rockchip/rk3399/drivers/m0/Makefile
+++ b/plat/rockchip/rk3399/drivers/m0/Makefile
@@ -53,7 +53,8 @@
 C_SOURCES		:= src/startup.c \
 			   src/main.c	\
 			   src/suspend.c \
-			   src/dram.c
+			   src/dram.c	\
+			   src/stopwatch.c
 
 # Flags definition
 CFLAGS			:= -g