[WIP] virt2real: disable mmc

When switching 3.9 -> 3.10 we need additional mmc workaround.

Just now there is a error:

  mmc0: host doesn't support card's voltages
  mmc0: error -22 whilst initialising MMC card
  mmc0: host doesn't support card's voltages
  mmc0: error -22 whilst initialising SDIO card
  mmc0: host doesn't support card's voltages

Signed-off-by: Antony Pavlov <antonynpavlov@gmail.com>