of: property: fw_devlink: Add support for firmware

Let fw_devlink create device links between consumers and suppliers of
firmware, and enforce these dependencies.

This prevents probing of drivers before the firmware they depend on
becomes available, thus avoiding unneeded probe deferrals.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
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Written for the upcoming R-Car X5H Clock Pulse Generator and Module
Controller drivers and their dependency on SCMI, but the existing
Raspberry Pi power domain driver should benefit from this, too.