It can be handy for example to add --strict option which can detect more
coding issues, even if not mandated by TF-A coding rules.
To use it:
 CHECKPATCH_OPTS="--strict" make checkpatch

Change-Id: I707e4cc2d1250b21f18ff16169b5f1e5ab03a7ed
Signed-off-by: Yann Gautier <yann.gautier@st.com>