target/platfrom: mdmfermium: map scratch region based on ddr size

Scratch region, size will be different for 128 and 256MB DDR varaints
of fermium targets. Added support to map these areas dynamically by
detecting the DDR size on the go.

Change-Id: I329e129ac8d476cdbc6dd38eb7277a31c660a323
3 files changed