nouveau: annotate public functions

This was done with:
nm --dynamic --defined-only build/nouveau/libdrm_nouveau.so | \
	grep nouveau_ | \
	cut -d ' ' -f3 > /tmp/a.txt

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. 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>
Acked-by: Eric Engestrom <eric.engestrom@intel.com>