ARM: dts: meson8b: odroidc1: add the CPU voltage regulator

The CPU voltage regulator is a "Monolithic Power Systems MP2161"
(according to the Odroid-C1+'s schematics). It is driven by PWM_C on
GPIODV_9.

Hardkernel's 3.10 kernel (based on the Amlogic GPL kernel sources)
defines a PWM voltage table with the following values:
- 0.86 volts = PWM register value 0x10f001b
- (more values in 0.1 volt increments)
- 1.14 volts = PWM register value 0x000012a
When using the XTAL (24MHz) as input this translates into a PWM period
of 12218ns with 0.86V using a duty cycle of 91% and 1.14V using a duty
cycle of 0%.

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>