boards: replace $HOST_DIR/usr/ with $HOST_DIR/ in scripts

Since things are no longer installed in $(HOST_DIR)/usr, the callers
should also not refer to it.

This is a mechanical change with
git grep -l 'HOST_DIR}\?/usr/' board | xargs sed -i 's%\(HOST_DIR}\?\)/usr/%\1/%g'

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>