Pali, I was doing the same. Even took the master from denx.de

Sometimes it does work and I see the emmc (but not the external sdcard).
I think the best change of getting it is start up o in plain maemo and then do a reboot (or power off) from the power-button menu.

I think it is just u-boot not properly initialising the twl403 MMC pins. I'm also looking at the linux kernel sources on how mmc is inititialised (e.g. the nokia patches) and it seems linux is doing a lot more stuff than u-boot does (e.g. initialising clocks).