ARM64: dts: rockchip: configure clock frequency for rk3399 tsadc

ARM64: dts: rockchip: configure clock frequency for rk3399 tsadc

As the rk3399 SoCs requires initial configuration for tsadc clock
frequency. The tsadc can be specified in a device tree node through
assigned-clocks.

The tsadc clock needs 500KHz~800KHz frequency to work on rk3399 SoCs.
We can add the assigned-clock to prevent the firmware
or loader has *not* set the division frequency from the source clock.

Change-Id: Ieb4cd5aad7d299baab20a9fb9d39211fe00896ff
Signed-off-by: Caesar Wang <wxt@rock-chips.com>