clk: rockchip: mark rk3399 GIC clocks as critical

We never want to kill the GIC.

Noticed when making other clock fixups, and seeing the newly-constructed
clock tree try to disable cpll, where we had this parent structure:

  aclk_gic <------\
                  |--- aclk_gic_pre <-- cpll <-- pll_cpll
  aclk_gic_noc <--/

Signed-off-by: Brian Norris <briannorris@chromium.org>
Reviewed-by: Douglas Anderson <dianders@chromium.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>