imx6: add Bachmann OT1200 board

This patch adds support for the OT1200 series of devices.

Following components are used in u-boot:
+ ethernet
+ i2c
+ emmc
+ gpio

For more details see README.

Changes v1 > v2
  - make use of enable_cspi_clock(..)
  - fix usage of OUTPUT_40OHM define
  - added README

Changes v2 > v3
  - improve spelling in README
  - added own copy of mx6q_4x_mt41j128.cfg

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>