qong: changes to Dave/DENX Qong configuration

1. Changes to the default environment:
  - "bootcmd" defined as "run flash_self"
  - "saveenv" command removed from "update"
  - "uboot" changed to "u-boot" (also in "load")
  - "addmtd" variable defined (and added to all boot commands)
2. CONFIG_CMD_JFFS2 defined to enable "mtdparts" command
3. MTDIDS_DEFAULT and MTDPARTS_DEFAULT defined
4. CONFIG_SYS_CBSIZE changed from 256 to 512. That solves the problem
with truncated "bootargs" environment variable.

Signed-off-by: Ilya Yanok <yanok@emcraft.com>