intel: annotate public functions

This was done with:
while read sym; do
	read f func line _ <<<$(cscope -d -L -1 $sym)
	if [ ! -z "$f" ]; then
		line=$((line-1))
		sed -i "${line}s/^/drm_public /" $f
	fi
done < /tmp/a.txt

Then some corner cases were manually fixed. "a.txt" above contains the
symbols collected from intel/intel-symbol-check. The idea here will be
to switch the default visibility to hidden so we don't export symbols we
shouldn't.

Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Eric Engestrom <eric.engestrom@intel.com>