ARM: mx6: ddr: Add support for iMX6UL/ULL/SL/SDL

This patch adds support for iMX6UL/ULL/SL/SDL MMDC into the DDR calibration
code. The difference between MX6DQ and MX6UL/ULL/SL is that the later SoCs
have 2 SDQS registers, just like MX6SX, while the MX6DQ/MX6SDL has 8.

Fixes: 4f4c128c65 ("ARM: mx6: ddr: Add support for iMX6SX")
Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Eric Nelson <eric@nelint.com>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>
Reviewed-by: Fabio Estevam <festevam@gmail.com>