ARM: AT91: DT: pm: Select ram controller standby based on DT

Move non-dt selection to ioremap_registers init which is only called not
non-dt board.

So we can support sam9n12/sam9x5/sama5d3 too.

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Nicolas Ferre <nicolas.ferre@atmel.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>