regulator: virtual: add devicetree support

regulator: virtual: add devicetree support

The reg-virt-consumer is very useful for development and testing of
regulator drivers since it allows voltages and modes to be set from
userspace.  However, it currently requires platform data so it cannot be
used without patching the kernel.  Add support for probing it from the
devicetree to remedy this.

Since this driver is only meant for testing and is a purely software
construct, no binding documentation is added.

Signed-off-by: Vincent Whitchurch <vincent.whitchurch@axis.com>
Link: https://lore.kernel.org/r/20220301111831.3742383-4-vincent.whitchurch@axis.com
Signed-off-by: Mark Brown <broonie@kernel.org>