of: Move of_prop_val_eq() next to the single user
There's only a single user of of_prop_val_eq(), so move it to overlay.c.
This removes one case of exposing struct property outside of the DT
code.
Signed-off-by: "Rob Herring (Arm)" <robh@kernel.org>
Link: https://lore.kernel.org/r/20250312212947.1067337-1-robh@kernel.org
Signed-off-by: Rob Herring (Arm) <robh@kernel.org>