Voltage divider
===============
When an iochannel measures the midpoint of a voltage divider, the
interesting voltage is often the voltage over the full resistance
of the divider. This binding describes the voltage divider in such
a curcuit.
Vin .

..
 R 
''

+ Vout

..
 Rout
''

GND
Required properties:
 compatible : "voltagedivider"
 iochannels : Channel node of a voltage iochannel measuring Vout.
 outputohms : Resistance Rout over which the output voltage is measured.
See fullohms.
 fullohms : Resistance R + Rout for the full divider. The iochannel
is scaled by the Rout / (R + Rout) quotient.
Example:
The system voltage is circa 12V, but divided down with a 22/222
voltage divider (R = 200 Ohms, Rout = 22 Ohms) and fed to an ADC.
sysv {
compatible = "voltagedivider";
iochannels = <&maxadc 1>;
/* Scale the system voltage by 22/222 to fit the ADC range. */
outputohms = <22>;
fullohms = <222>; /* 200 + 22 */
};
&spi {
maxadc: adc@0 {
compatible = "maxim,max1027";
reg = <0>;
#iochannelcells = <1>;
interruptparent = <&gpio5>;
interrupts = <15 IRQ_TYPE_EDGE_RISING>;
spimaxfrequency = <1000000>;
};
};