rockchip: rk356x-u-boot: Set max-frequency prop in sdhci node

Most board device trees for RK356x set max-frequency = <200000000> in
the sdhci node, some boards like Quartz64 do not. This result in an
error message due to sdhci driver trying to set a clock rate of 0
instead of the max-frequency value.

  rockchip_sdhci_probe clk set rate fail!

Fix this by setting a common max-frequency in rk356x-u-boot.dtsi. A
patch to set default max-frequency of sdhci node in linux is planned.

Also remove the forced status = "okay" for the sdhci and sdmmc0 nodes,
boards already set correct state for these nodes.

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