ARM: dts: exynos: add a specific compatible to MCT

One compatible is used for the Multi-Core Timer on most of the Samsung
Exynos SoCs, which is correct but not specific enough.  These MCT blocks
have different number of interrupts, so add a second specific
compatible to Exynos3250 and all Exynos5 SoCs.

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Reviewed-by: Alim Akhtar <alim.akhtar@samsung.com>
Link: https://lore.kernel.org/r/20220304122424.307885-3-krzysztof.kozlowski@canonical.com