ARM: at91: remove useless at91rm9200_set_type()

Since all rm9200 board files have been removed, there is no user of
at91rm9200_set_type() left. Remove it

Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Acked-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>