Implement a nice generalization suggested by Bobby Noelte.
Instead of having a generic #cells key in bindings, have source-specific
*-cells keys. Some examples:
interrupt-cells:
- irq
- priority
- flags
gpio-cells:
- pin
- flags
pwm-cells:
- channel
- period
This makes bindings a bit easier to read, and allows a node to be a
controller for many different 'phandle-array' properties.
The prefix before *-cells is derived from the property name, meaning
there's no fixed set of *-cells keys. This is possible because of the
earlier 'phandle-array' generalization.
The older #cells key is supported for backwards compatibility, but
generates a deprecation warning.
Signed-off-by: Ulf Magnusson <Ulf.Magnusson@nordicsemi.no>