refactor(st-ddr): move basic tests in a dedicated file

These basic tests are generic and should be used independently of the
driver, depending on the plaftorm characteristics.

Change-Id: I38161b659ef2a23fd30a56e1c9b1bd98461a2fe4
Signed-off-by: Nicolas Le Bayon <nicolas.le.bayon@foss.st.com>
4 files changed