clk: rockchip: describe clk_gmac using the new muxgrf type on rk3328

With the newly introduced clk type for muxes in the grf we now can
describe some missing clocks, like the clk_gmac2io and clk_gmac2phy
that selects between clk_mac2io_src and gmac_clkin based on a bit
set in the general register files.

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>