mci_of_parse takes care of the generic oftree bits, like removable flag,
aliases and max-frequency. Insert it, so we can start to refer to the
controller's block devices by a fixed name.

Sticking in the mci_of_parse shows that the SD/MMC2 driver in barebox
doesn't play nicely with the device tree specification of the SD/MMC2
for the dk2 board, however:

Specifying the bus-width = <4> property in the device tree now made mmc
usage fail when reading the environment:

  ERROR: error SDMMC_STA_DCRCFAIL (0x81042) for cmd 18
  ERROR: stm32_sdmmc2_end_cmd: error SDMMC_STA_CTIMEOUT (0x4) for cmd 12
  WARNING: stm32_sdmmc2_send_cmd: cmd 12 failed, retrying ...
  ERROR: stm32_sdmmc2_end_cmd: error SDMMC_STA_CTIMEOUT (0x4) for cmd 12
  WARNING: stm32_sdmmc2_send_cmd: cmd 12 failed, retrying ...
  ERROR: stm32_sdmmc2_end_cmd: error SDMMC_STA_CTIMEOUT (0x4) for cmd 12
  WARNING: stm32_sdmmc2_send_cmd: cmd 12 failed, retrying ...
  ERROR: stm32_sdmmc2_end_cmd: error SDMMC_STA_CTIMEOUT (0x4) for cmd 12

We'll want to fix this eventually, but for now force the bus width to 1.
So we don't forget about this, print a notice to the console that we've
done so.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>