Fix bug 6149: Wrong TEEC_VERSION definition

Change-Id: I0df330584e229e0e9400aa204010d07c74f0da3e
Signed-off-by: Fabrice Couteau <fabrice.couteau@st.com>
Reviewed-on: https://gerrit.st.com/8722
Reviewed-by: Pascal BRAND <pascal.brand@st.com>
Reviewed-by: Emmanuel MICHEL <emmanuel.michel@st.com>
Cleanup Makefile

- Add missing rootfs_clean rule
- Remove unused defines
- Rename some rules

This fix #6 (GitHub issue)

Signed-off-by: Pascal Brand <pascal.brand@st.com>