pkg-download: silence downloads if make is silent

If doing a silent build (make -s -> QUIET=-q), silence all downloads,
by passing the -q flag downward to backends as well as to check-hash.

Change a printf to use the trace functions.

Signed-off-by: Fabio Porcedda <fabio.porcedda@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>