mmc: dw_mmc: Add MSHC compatible for Exynos4412

This patch adds the compatible string for MSHC controller of Exynos4412.
And exynos5250_dwmmc_caps is renamed to exynos_dwmmc_caps, since it has the
capabilities of common features supported by Exynos4 and Exynos5.

Signed-off-by: Dongjin Kim <tobetter@gmail.com>
Acked-by: Seungwon Jeon <tgih.jun@samsung.com>
Signed-off-by: Chris Ball <cjb@laptop.org>