mtd: nand: Remove docg4 driver and palmtreo680 flashing tool

Commit ad4f54ea ("arm: Remove palmtreo680 board") removed the only
user of the docg4 driver and the palmtreo680 image flashing tool.  This
patch removes them.

Signed-off-by: Scott Wood <oss@buserror.net>
Cc: Mike Dunn <mikedunn@newsguy.com>
Cc: Simon Glass <sjg@chromium.org>