clk: rockchip: add support for phase inverters

Most Rockchip socs have optional phase inverters connected to some
clocks that move the clock-phase by 180 degrees.

Signed-off-by: Heiko Stuebner <heiko@sntech.de>
[sboyd@codeaurora.org: Dropped lazy part of commit text]
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>