exynos5: split out mobicore driver variants

Currently supported are Exynos5420 and non-Exynos5420
(which really is manta->Exynos5250).

The Exynos5420 driver was taken from ODROID-XU 04212014 BSP

Change-Id: I82450356e72e766b01f68d0398788e4bbad4ae1e
exynos5: cover more vsync attribute paths for different Exynos revisions

Added two new vsync paths to cover all currently known Exynos variants.

Change-Id: I1382083537e37e6591799f4ee725eaa7a87fbb56