at91: drop at572d940hf support

no-one use it and it's nearly impossible get a board to work on it
and the Mainline implementation was never finished

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Cc: Patrice Vilchez <patrice.vilchez@atmel.com>
Cc: Andrew Victor <linux@maxim.org.za>