Add helpers for exception debug on AARCH32

New helper functions are created to handle undefined instructions,
data & prefetch aborts in AARCH32. They call platform functions,
just like what report_exception is doing.
Those new helpers are created mainly to distinguish data and prefetch
aborts, as they both share the same mode.

Change-Id: I5dd31930344ad4e3a658f8a9d366a87a300aeb67
Signed-off-by: Yann Gautier <yann.gautier@st.com>