arm64: dts: rockchip: fix RockPro64 sdhci settings

arm64: dts: rockchip: fix RockPro64 sdhci settings

The RockPro64 schematics [1], [2] show that the rk3399 EMMC_STRB pin is
connected to the RESET pin instead of the DATA_STROBE pin of the eMMC module.
So the data strobe cannot be used for its intended purpose on this board,
and so the HS400 eMMC mode is not functional. Limit the controller to HS200.

[1] http://files.pine64.org/doc/rockpro64/rockpro64_v21-SCH.pdf
[2] http://files.pine64.org/doc/rock64/PINE64_eMMC_Module_20170719.pdf

Fixes: d0b34973932d ("arm64: dts: rockchip: add initial dts support for Rockpro64")
Signed-off-by: Soeren Moch <smoch@web.de>
Link: https://lore.kernel.org/r/20191003215036.15023-2-smoch@web.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>