Bluetooth: Add overlay for bt voltage

Setting the operating voltage value in the
platform-specific config overlay via
"config_bluetooth_operating_voltage_mv" and depends
on the voltage value that Controller took into account
while calculating/reporting the energy to Battery meter

CRs-Fixed: 923054
Change-Id: I9671cf46b68e86e5a2d58b65ab158f774c997433
1 file changed