mmc: dw_mmc: move rockchip related code to a separate file

To support HS200 and UHS-1, we need add a big hunk of code,
as shown in the following patches. So a separate file for
rockchip SOCs is suitable.

Signed-off-by: Addy Ke <addy.ke@rock-chips.com>
Acked-by: Jaehoon Chung <jh80.chung@samsung.com>
Tested-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Doug Anderson <dianders@chromium.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
diff --git a/drivers/mmc/host/Kconfig b/drivers/mmc/host/Kconfig
index a43295c..1386065 100644
--- a/drivers/mmc/host/Kconfig
+++ b/drivers/mmc/host/Kconfig
@@ -638,6 +638,15 @@
 
 	  If unsure, say N.
 
+config MMC_DW_ROCKCHIP
+	tristate "Rockchip specific extensions for Synopsys DW Memory Card Interface"
+	depends on MMC_DW && ARCH_ROCKCHIP
+	select MMC_DW_PLTFM
+	help
+	  This selects support for Rockchip SoC specific extensions to the
+	  Synopsys DesignWare Memory Card Interface driver. Select this option
+	  for platforms based on RK3066, RK3188 and RK3288 SoC's.
+
 config MMC_SH_MMCIF
 	tristate "SuperH Internal MMCIF support"
 	depends on MMC_BLOCK && HAS_DMA