ARM: dts: bcm283x: switch from &sdhci to &sdhost

sdcard access with the sdhost controller is faster.

Read access (dd with 64k blocks on rpi2):
   CONFIG_MMC_SDHCI_IPROC: 11-12 MB/s
   CONFIG_MMC_BCM2835:     19-20 MB/s

Differences on write access are pretty much in the noise.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Acked-by: Eric Anholt <eric@anholt.net>