arm, am33xx: update for siemens am335x based boards

updates for the siemens am335x based boards:

- draco: add delay for DDR3 configuration
- change MTD partition layout and add a possibility
  to redefine MTD layout in board header.
- move ubi support to common header file
- draco: improve dtb naming
- draco: set CONFIG_SYS_CBSIZE to 1024
- add generic env based led
  Leds can now be defined in Environment
- add generic env based dfu button
  Which gpio is used for the dfu button can be defined
  through the Environment
- set MACH_TYPE only if defined
- draco: increase CPU freq to 300MHz
- Add time command to siemens am33xx boards
- DDR3: increase default tRFC
- draco: enable pullup for DFU and ERST pin
- change print format DDR3

Signed-off-by: Samuel Egli <samuel.egli@siemens.com>
Acked-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>

Signed-off-by: Heiko Schocher <hs@denx.de>