Remove the previously use function: get_timer, and use new functions
timeout_init_us and timeout_elapsed.

Change-Id: I4e95b123648bff7ca91e40462a2a3ae24cfe1697
Signed-off-by: Yann Gautier <yann.gautier@st.com>
Signed-off-by: Etienne Carriere <etienne.carriere@st.com>
Signed-off-by: Nicolas LE BAYON <nicolas.le.bayon@st.com>