arm64: dts: rockchip: add rk3368 tuning clk for emmc and sdmmc

Add tuning clk for emmc and sdmmc, otherwise I get
the following failure while enabling mmc-hs200-1_8v.

dwmmc_rockchip ff0f0000.dwmmc: Tuning clock (sample_clk) not defined.
mmc0: tuning execution failed
mmc0: error -5 whilst initialising MMC card

With it
dwmmc_rockchip ff0f0000.dwmmc: Successfully tuned phase to 170
mmc0: new HS200 MMC card at address 0001
mmcblk0: mmc0:0001 M8G1GC 7.28 GiB

Signed-off-by: Shawn Lin <shawn.lin@rock-chips.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>