ARM: EXYNOS: Remove a new bus_type instance for EXYNOS5

A seperate bus_type instance is not required for EXYNOS5. The
existing bus_type instance used with EXYNOS4 is sufficient for
both EXYNOS4 and EXYNOS5. This also solves issue of uninitialized
usage of exynos4_subsys in EXYNOS4 power management code that is
reused for EXYNOS5 also. In addition to that, the existing
exynos4_subsys bus_type is renamed to exynos_subsys to indicate
that it is reused on both EXYNOS4 and EXYNOS5 platforms.

Signed-off-by: Thomas Abraham <thomas.abraham@linaro.org>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>