clk: rockchip: Add new pll type pll_rk3588_ddr

That PLL type is similar to the other rk3588 pll types but the actual
rate is twice the configured rate.
Therefore, the returned calculated rate must be multiplied by two.

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Signed-off-by: Detlev Casanova <detlev.casanova@collabora.com>
Acked-by: Dragan Simic <dsimic@manjaro.org>
Link: https://lore.kernel.org/r/0102019199a76ec4-9d5846d4-d76a-4e69-a241-c88c2983d607-000000@eu-west-1.amazonses.com


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