Replace Rockchip delay timer by generic one

Use the generic delay timer instead of having a specific platform
file for configuring it.

Change-Id: Ifa68b9c97cd96ae1190cee74d22d729af95e4537
diff --git a/plat/rockchip/rk3368/platform.mk b/plat/rockchip/rk3368/platform.mk
index 0d34cf4..0e64b7e 100644
--- a/plat/rockchip/rk3368/platform.mk
+++ b/plat/rockchip/rk3368/platform.mk
@@ -58,13 +58,13 @@
 				drivers/console/console.S			\
 				drivers/ti/uart/16550_console.S			\
 				drivers/delay_timer/delay_timer.c		\
+				drivers/delay_timer/generic_delay_timer.c	\
 				lib/cpus/aarch64/cortex_a53.S			\
 				plat/common/aarch64/platform_mp_stack.S		\
 				${RK_PLAT_COMMON}/aarch64/plat_helpers.S	\
 				${RK_PLAT_COMMON}/bl31_plat_setup.c		\
 				${RK_PLAT_COMMON}/pmusram/pmu_sram_cpus_on.S		\
 				${RK_PLAT_COMMON}/pmusram/pmu_sram.c		\
-				${RK_PLAT_COMMON}/plat_delay_timer.c		\
 				${RK_PLAT_COMMON}/plat_pm.c			\
 				${RK_PLAT_COMMON}/plat_topology.c		\
 				${RK_PLAT_COMMON}/aarch64/platform_common.c	\