Thank you for the response, Stefan!
I had already some doubt whether my calculation was correct. After a long day, I was too tired to think it over again, and set the byte before and the one after too, just to be on the save side. (Maybe I should have mentioned this.) Today I set only byte 47.
Code:
[root@(none) ~]# ntx_hwconfig -s /dev/mmcblk1
...
[0] PCB='E60610D'
...
[47] BootOpt='[+] 0x01'
...
[root@(none) ~]# cat /proc/cmdline
console=ttymxc0,115200 rootwait rw quiet lpj=3997696 root=/dev/mmcblk0p1 rootfst
ype=ext4 hwcfg_p=0x7ffffe00 hwcfg_sz=512 waveform_p=0x7fefd000 waveform_sz=10603
52 mem=254M