mmc: dw_mmc: exynos: move definitions to header file

Move exynos related definition to header file. And this
also changes some of the registers name to match the standard
naming convention.

Signed-off-by: Seungwon Jeon <tgih.jun@samsung.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
[Alim: updated the commit message]
Signed-off-by: Alim Akhtar <alim.akhtar@samsung.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>