ARM: exynos: Set MCPM as mandatory for Exynos542x/5800 SoCs

Support for Exynos5420/5422/5800 SoCs requires MCPM to properly boot all
CPU cores on all currectly supported platforms: Peach Pit (Exynos5420),
Odroid XU3/XU3lite/XU4/HC1 (Exynos5422) and Peach Pi (Exynos5800).
Without it some CPU cores fail to come online. Remove then the ability to
disable MCPM and make it mandatory when Exynos542x/5800 support is
enabled.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>