After being introduced 3 years ago this feature ended up being
"obsoleted by events" and project it was supposed to be a part of
winded down.

Revert this feature due to:

  a) Lack of users

  b) Existence of better way to make barebox load via SRAM as
  intermediary step that does not require two separate images to be
  built (.imx-sram-img)

This reverts commit 903c947.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>