dt-bindings: arm: samsung: add compatibles for exynos7870 devices

dt-bindings: arm: samsung: add compatibles for exynos7870 devices

Document the compatible string for Exynos7870 - "samsung,exynos7870".

The following devices are also added:
 - Galaxy A2 Core       ("samsung,a2corelte")
 - Galaxy J6            ("samsung,j6lte")
 - Galaxy J7 Prime      ("samsung,on7xelte")

Acked-by: Rob Herring (Arm) <robh@kernel.org>
Signed-off-by: Kaustabh Chakraborty <kauschluss@disroot.org>
Link: https://lore.kernel.org/r/20250501-exynos7870-v7-1-bb579a27e5eb@disroot.org
Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>