The weak mxs_adjust_memory_params function is called from spl_mem_init.c,
so it must be linked into the SPL to have an effect. Move it from
mx23_olinuxino.c to spl_boot.c.

This change was verified by reading back the register values.

Signed-off-by: Jan Luebbe <jlu@pengutronix.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Stefano Babic <sbabic@denx.de>