ACLK_VIO is the noc bus clock for display module, display cann't
read data from ddr without this clock enabled.

Due to it shouldn't belong to any driver, but we need it enabled,
so just mark it as the CLK_IGNORE_UNUSED flag.
Signed-off-by: NYakir Yang <ykk@rock-chips.com>
Signed-off-by: NCaesar Wang <wxt@rock-chips.com>
Signed-off-by: NHeiko Stuebner <heiko@sntech.de>