ARM: at91: Change the internal SRAM memory type MT_MEMORY_NONCACHED

Because MT_DEVICE is not executable in armv7, we change
the internal SRAM memory type to MT_MEMORY_NONCACHED.
As it seems that caching this internal SRAM memory is not necessary,
we chose the this memory type.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>