Unannounced 12.1.0 devel build 4 does not boot on XO-1

[Mikus Grinbergs]

Used 'update-nand' to write os4 onto XO-1.  With Q2F07 I get:

  |  Boot device: /nandflash:\boot\olpc.fth  Arguments:
  |  Boot device: /pci/nandflash at c\boot\vmlinuz  Arguments:
  |  <buffer at ffb5d500>:88:
  |  Can't open boot device

With os3 (and Q2F07) the two "Boot device" lines are followed by

  !  Loading ramdisk image ...


mikus