ARM: imx: vining2000: Convert MMC and block to DM

Enable DM block and DM MMC support on iMX6SX VINING|2000 .
Convert board code to match the DM support. This disables
USB mass storage support due to missing DM USB, however
that will be re-enabled in subsequent patch.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Silvio Fricke <silvio.fricke@softing.com>
Cc: Stefano Babic <sbabic@denx.de>