ARM: dts: exynos: Properly select eMMC HighSpeed mode on Odroid XU

Exynos5410 supports eMMC version 4.41 so HS200 is the top mode which
should be configured.  This is reflected in usage of
"samsung,exynos5250-dw-mshc" compatible.  However Odroid XU DTS
contained also property "mmc-hs400-1_8v" which is parsed by MMC core
therefore resulting in mixed configuration.  MMC core set HS400 but
dwmmc_exynos driver did not configure the data strobe for HS400 DDR
mode.

Removal of HS400 properties fixes semi-random mmc errors during boot:
  mmc_host mmc0: Bus speed (slot 0) = 400000000Hz (slot req 200000000Hz, actual 200000000HZ div = 1)
  mmc0: mmc_select_hs400 failed, error -84
  mmc0: error -84 whilst initialising MMC card

Signed-off-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>