ARM: at91/pm: move the copying the sram function to the sram initialization phase

To decrease the suspend time, move copying the sram function to the sram
initialization phase, instead of every time go to suspend.

In the meanwhile, substitute fncpy() for memcpy().

If there is no sram allocated for PM, the PM is not supported.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Acked-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>
Tested-by: Sylvain Rochet <sylvain.rochet@finsecur.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>