ARM: dts: exynos: rename from EXYNOS5_DWMMC to EXYNOS_DWMMC

Exynos serise can be supported the dw-mmc controller.
So, it's good that used the general prefix as "_EXYNOS_DWMMC".

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>