clk: rockchip: Optimize PLL table memory usage

clk: rockchip: Optimize PLL table memory usage

Before the change: The sizeof rk3568_pll_rates = 2544
Use union: The sizeof rk3568_pll_rates = 1696

In future Soc, more PLL types will be added, and the
rockchip_pll_rate_table will add more members,
and the space savings will be even more pronounced
by using union.

Signed-off-by: Elaine Zhang <zhangqing@rock-chips.com>
Link: https://lore.kernel.org/r/20210511090726.15146-1-zhangqing@rock-chips.com
Signed-off-by: Heiko Stuebner <heiko@sntech.de>