ARM: mx6: Handle the MMDCx_MDCTL COL field caprices

The COL field value cannot be easily calculated from the desired
column number. Instead, there are special cases for that, see the
datasheet, MMDCx_MDCTL field description, field COL . Cater for
those special cases.

Signed-off-by: Marek Vasut <marex@denx.de>