arm64: dts: rockchip: add overlay test for Edgeble NCM6A/NCM6B

arm64: dts: rockchip: add overlay test for Edgeble NCM6A/NCM6B

The Edgeble NCM6A/NCM6B can have WiFi modules connected and this is
handled via an overlay (commit 951d6aaa37fe ("arm64: dts: rockchip: Add
Edgeble NCM6A WiFi6 Overlay")).

Despite the name of the overlay, it applies to both NCM6A and NCM6B[1].

In order to make sure the overlay is still valid in the future, let's
add a validation test by applying the overlay on top of the main bases
at build time.

[1] https://lore.kernel.org/linux-rockchip/CA+VMnFyom=2BmJ_nt-At6hTQP0v+Auaw-DkCVbT9mjndMmLKtQ@mail.gmail.com/

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Reviewed-by: Jagan Teki <jagan@edgeble.ai>
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Link: https://lore.kernel.org/r/20250211-pre-ict-jaguar-v6-2-4484b0f88cfc@cherry.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>