clk: rockchip: rk3399: Improve support for SCLK_PCIEPHY_REF clock

clk: rockchip: rk3399: Improve support for SCLK_PCIEPHY_REF clock

rk3399-nanopi-4.dtsi try to set parent of and set rate to 100 MHz of the
SCLK_PCIEPHY_REF clock.

The existing enable/disable ops for SCLK_PCIEPHY_REF currently force
use of 24 MHz parent and rate.

Add improved support for setting parent and rate of the pciephy refclk
to driver to better support assign-clock props for pciephy refclk in DT.

This limited implementation only support setting 24 or 100 MHz rate,
and expect npll and clk_pciephy_ref100m divider to use default values.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>