u-boot: use all 256MB of NAND

[Werner Almesberger]

u-boot's dynpart only used half the NAND available in GTA02.
That's fixed in revision 4047.

- Werner

----------------------------------- Changes -----------------------------------

uboot-gta02.patch:
- board/neo1973/gta02/gta02.c (dynpart_size): sized don't need to add up to
  exactly the nominal size
- board/neo1973/gta02/gta02.c (dynpart_size): changes size of rootfs from 128MB
  to 256MB