libs/utils/energy: do not requires a "conf" entry for iio-capture's defaults
libs/utils/energy: do not requires a "conf" entry for iio-capture's defaults

Make optional the "conf" section for iio-capture emeters setup in case
the defaults are to be used.

Signed-off-by: Patrick Bellasi <431c86f368affbc3148c4669fbd465131f7e82cb@arm.com>

mdigiorgio/lisa,ARM-software/lisa,bjackman/lisa,credp/lisa,mdigiorgio/lisa,arnoldlu/lisa,credp/lisa,credp/lisa,joelagnel/lisa,arnoldlu/lisa,credp/lisa,ARM-software/lisa,bjackman/lisa,joelagnel/lisa,ARM-software/lisa,ARM-software/lisa