ARM: tegra: dts: cardhu: enable SLINK4

Enable SLINK4 and connected device in Tegra30 based
platform Cardhu.
Setting maximum spi frequency to 25MHz.

SPI serial flash is connected on CS1 of SLINK4 on
cardhu platform.

Signed-off-by: Laxman Dewangan <ldewangan@nvidia.com>
[swarren: swapped reg/compatible order to be consistent]
Signed-off-by: Stephen Warren <swarren@nvidia.com>