servo: add 1.8V supply for ZerbleBarn

Mimick the DragonTalon configuration and use the spi2_vref as the 1.8V
power supply for the sensors (in the case with a flying wire from J13
pin 5)

TEST=run servod with 'sudo servod -b zerblebarn -c zerblebarn_inas.xml'
a fingerprint capture with 'fpcapture' on the serial console works,
'dut-control pp1800_fpc_mv' returns something close to 1.8V.

Change-Id: I00fa6c2febe0035f546678c63c237699b6f83606
Commit-Ready: Vincent Palatin <>
Tested-by: Vincent Palatin <>
Reviewed-by: Vincent Palatin <>
1 file changed