mx28evk: Convert to mxs_adjust_memory_params()

Recent conversion from mx28_adjust_memory_params to mxs_adjust_memory_params
missed to update mx28evk, which caused the board not to boot.

Apply the conversion so that the board can boot again.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Marek Vasut <marex@denx.de>