Hello,wysockilukasz,
The modification you did is not enough, Paralell nor flash will use WEIM interface of i.mx51, normally it has 25bit or 26bit address line and 16bit data lines, for example , probably you will use EIM_DA0~EIM_DA15 and EIM_A16~EIM_A25 to be address lines, and EIM_D16~EIM_D31 is used to be data lines; EIM_OE is reading signal, EIM_RW is writing signal, EIM_CS0 is used as chipselect, So you will configure these pins in u-boot/board/freescale/mx51_bbg/mx51_bbg.c :
(1)IOMUX all pins you will use.
(2)Setting IOMUX mode( such as 16bit non-mux mode etc)
(3)Setting work mode (maybe it works as asysncronous mode)
(4)Setting total capacities on EIM_CS0 and disable other EIM_CSx.
For mode detail, please refer to weim interface in mcimx51RM.pdf
Then on hardware, you should set boot_mode0 & boot_mode1 pin to be internal mode. and set corresponding EIM PINs to boot from Parallel NOR Flash connected to WEIM interface.
Regards,
Weidong