ARM: davinci: fixes for cam_enc_4xx board

- change CONFIG_ENV_RANGE to contain 2 nand erase blocks,
  one for bad block reserve.
- remove from the envvariable "img_writeramdisk" the
  ubifsmount command, as it is not needed.
- erase the hole mtd partition containing u-boot
- save environment variable "dvn_app_vers" and "dvn_boot_vers"
  only after installing the new image.
changes requested from Marek Vasut:
- arm, davinci: fix eldk-4.2 warnings for cam_enc_4xx board
  - get rid of run_command2 usage
    needed since patch:
    commit 009dde19
    Author: Simon Glass <sjg@chromium.org>
    Date:   Tue Feb 14 19:59:20 2012 +0000

    Rename run_command2() to run_command()
    is now in mainline.
  - add CONFIG_SPL_LIBGENERIC_SUPPORT support
  - remove CONFIG_CMD_PXE support
  - fix warning:
    cam_enc_4xx.c: In function 'menu_handle':
    cam_enc_4xx.c:609: warning: dereferencing type-punned pointer
    will break strict-aliasing rules
  - fix error:
    arm-linux-ld: u-boot-spl: Not enough room for program headers,
    try linking with -N

Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Tom Rini <tom.rini@gmail.com>
Cc: Fletzer Martin <Martin.Fletzer@ait.ac.at>
Cc: Wolfgang Denk <wd@denx.de>