Platform/ARM/N1Sdp: Introduce platform DXE driver

Add an initial platform DXE driver and support for ramdisk devices.

Change-Id: Idf61fdc3dbde384e0414a80739078bb206784fc3
Signed-off-by: Deepak Pandey <Deepak.Pandey@arm.com>
Signed-off-by: Khasim Syed Mohammed <khasim.mohammed@arm.com>