i.MX6ULL has errata ERR010450, point out that due to SOC I/O
timing limitation, for eMMC HS200 and SD/SDIO 3.0 SDR104, the
clock rate can't exceed 150MHz. And for eMMC DDR52 and SD/SDIO
DDR50 mode, the clock rate can't exceed 45MHz.

This patch add this limit for imx6ull.

Signed-off-by: Haibo Chen <haibo.chen@nxp.com>
Acked-by: Adrian Hunter <adrian.hunter@intel.com>
[Ulf: Fixed comments and whitespace]
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>