feat(st): mandate dtc version 1.4.7

To be able to use /omit-if-no-ref/ in DT files, the dtc version should
be at least 1.4.7. Update the makefile rule that checks dtc version.

Signed-off-by: Yann Gautier <yann.gautier@st.com>
Change-Id: I06bde289cf359a7383694e4c86991dfba781e7d7
1 file changed