soc: nordic: common: dmm: Fix memory utilization

DMM was enforcing cache line alignment all memory regions, including
those which were not cacheable. Fixing it by using memory attribute
from the device tree to determine if alignment needs to be applied.

Because of that memory usage was significantly increased because
even 1 byte buffers (e.g. for uart_poll_out) was consuming 32 bytes
(cache line size).

Signed-off-by: Krzysztof Chruściński <krzysztof.chruscinski@nordicsemi.no>