arm64: dts: rockchip: add overlay tests for Rock 5B PCIe overlays

arm64: dts: rockchip: add overlay tests for Rock 5B PCIe overlays

According to commit 40658534756f ("arm64: dts: rockchip: Add rock5b
overlays for PCIe endpoint mode"), Rock 5B can operate in PCIe endpoint
mode. For that to work, the rk3588-rock-5b-pcie-ep.dtbo overlay needs to
be applied on Rock 5B base Device Tree. If that Rock 5B is connected to
another Rock 5B, the latter needs to apply the
rk3588-rock-5b-pcie-srns.dtbo overlay.

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

Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Niklas Cassel <cassel@kernel.org>
Reviewed-by: Dragan Simic <dsimic@manjaro.org>
Signed-off-by: Quentin Schulz <quentin.schulz@cherry.de>
Link: https://lore.kernel.org/r/20250211-pre-ict-jaguar-v6-3-4484b0f88cfc@cherry.de
Signed-off-by: Heiko Stuebner <heiko@sntech.de>