board: da8xxevm: Add SPL DM for serial, spi

This patch add SPL DM support for da8xxevm boards
with SPL serial, SPI drivers supported via platdata.

Cc: Adam Ford <aford173@gmail.com>
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Adam Ford <aford173@gmail.com> #da850evm