max5847: add sample

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
doyxgen: make layout show brief seperately

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>
doc: improve & complete documentation on many sensors

Signed-off-by: Brendan Le Foll <brendan.le.foll@intel.com>