clk: rockchip: describe aclk_vcodec using the new muxgrf type on rk3288

With the newly introduced clk type for muxes in the grf we now can
describe some missing clocks, like the aclk_vcodec that selects between
aclk_vdpu and aclk_vepu based on a bit set in the general register files.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>