Update rockchip platform to not rely on undefined overflow behaviour

This consists of ensuring that the left operand of each shift is
unsigned when the operation might overflow into the sign bit.

Change-Id: Ib7fc54e4141cc4f1952a18241bc18671b36e2168
Signed-off-by: Justin Chadwell <justin.chadwell@arm.com>
diff --git a/plat/rockchip/rk3368/drivers/soc/soc.h b/plat/rockchip/rk3368/drivers/soc/soc.h
index 5f24e93..6c7a01b 100644
--- a/plat/rockchip/rk3368/drivers/soc/soc.h
+++ b/plat/rockchip/rk3368/drivers/soc/soc.h
@@ -50,7 +50,7 @@
 #define PMUSRAM_S		1
 #define STIMER_S_SHIFT		6
 #define STIMER_S		1
-#define SGRF_SOC_CON7_BITS	((0xffff << 16) | \
+#define SGRF_SOC_CON7_BITS	((0xffffu << 16) | \
 				 (PMUSRAM_S << PMUSRAM_S_SHIFT) | \
 				 (STIMER_S << STIMER_S_SHIFT))