arm, am335x: update for the siemens boards

- dxr2: define unused pins as input
- do not enable RTC32K OSC on dxr2 board
- update default environment
  - add splashpos=m,m to default environment, so splash screen is always
    centered.
  - adapt environment for bootcount feature
  - add altbootcmd to default environment
- rut: SPL add early reset pulse for eth-phy, maXTouch and display
- rut: display timing aenderungen
- siemens boards: adapt for background color = white
- add boutcount feature for the siemens boards
  store the bootcount in the environment, as we have no softreset
  save registers on this hardware. Use therefore the CONFIG_BOOTCOUNT_ENV
  bootcount driver.
- change spi mode from 3 to 0 for the lcd init
- add gpio pin for lcd reset with state 0 and add mdelay
- siemens boards: use own USB id's
- add dfu serial and device number for siemens boards
  Add for the siemens boards the possibility to define in dfu mode,
  the iSerialNumber and the bcdDevice fields in the USB Device
  descriptor.
- fix upgrade mechanism based on bootcount
  Correct location of saveenv and remove not active variable.

  Add CONFIG_BOOT_RETRY_TIME and CONFIG_RESET_TO_RETRY to
  reboot board in case of empty kernel partition. Without
  these defines an empty kernel partition leads to an
  abort of boot process and one remains in u-boot prompt.

- general cleanup of dxr2, pxm2 and rut boards
  all:
   * Remove net boot from bootcmd
     Ping can cause a crash on boards without ethernet phy.
     net_nfs command is used only for development

   * Add reset at the end of bootcmd
     In order to have an immediate reset of the boot when bootcmd
     fails, add reset at the end of bootcmd.

  rut:
   * add nand_img_size

  dxr2:
   * update nand_img_size

   * ddr3 timings updated with iocontrol property that can be
     modified via eeprom. New default parameters from software
     leveling with draco ES2.

Signed-off-by: Samuel Egli <samuel.egli@siemens.com>
Signed-off-by: Pascal Bach <pascal.bach@siemens.com>
Signed-off-by: Roger Meier <r.meier@siemens.com>
Signed-off-by: Heiko Schocher <hs@denx.de>
Cc: Matthias Michel <matthias.michel@siemens.com>
Cc: Tom Rini <trini@ti.com>