clk: rockchip: add a factor clock type

clk: rockchip: add a factor clock type

Add a clock type for fixed factor clocks. This allows us to define fixed
factor clocks where they appear in the clock hierarchy instead of in the
init function.

The additional factor_gate type, finally allows us to model some last
parts of the clock tree correctly.

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