rockchip: Exclude rk_timer for ARM64

It conflicts with the generic_timer.

Cc: Kever Yang <kever.yang@rock-chips.com>
Signed-off-by: Andreas Färber <afaerber@suse.de>
Acked-by: Simon Glass <sjg@chromium.org>

arch/arm/mach-rockchip/Makefile

@@ -11,6 +11,8 @@ obj-$(CONFIG_ROCKCHIP_SPL_BACK_TO_BROM) += save_boot_param.o
 else
 obj-$(CONFIG_ROCKCHIP_RK3288) += board.o
 endif
+ifndef CONFIG_ARM64
 obj-y += rk_timer.o
+endif
 obj-$(CONFIG_ROCKCHIP_RK3288) += rk3288/
 obj-$(CONFIG_ROCKCHIP_RK3036) += rk3036/