mmc: sdhci: move the ADMA2 table handling into own module

There are other (non-SDHCI) controllers which supports ADMA2 descriptor
tables, namely the Freescale eSDHC. Instead of copying the code, move it
into an own module.

Signed-off-by: Michael Walle <michael@walle.cc>
diff --git a/drivers/mmc/Kconfig b/drivers/mmc/Kconfig
index 0c252e3..88582db 100644
--- a/drivers/mmc/Kconfig
+++ b/drivers/mmc/Kconfig
@@ -46,6 +46,9 @@
 
 if MMC
 
+config MMC_SDHCI_ADMA_HELPERS
+	bool
+
 config MMC_SPI
 	bool "Support for SPI-based MMC controller"
 	depends on DM_MMC && DM_SPI
@@ -445,6 +448,7 @@
 config MMC_SDHCI_ADMA
 	bool "Support SDHCI ADMA2"
 	depends on MMC_SDHCI
+	select MMC_SDHCI_ADMA_HELPERS
 	help
 	  This enables support for the ADMA (Advanced DMA) defined
 	  in the SD Host Controller Standard Specification Version 3.00
@@ -452,6 +456,7 @@
 config SPL_MMC_SDHCI_ADMA
 	bool "Support SDHCI ADMA2 in SPL"
 	depends on MMC_SDHCI
+	select MMC_SDHCI_ADMA_HELPERS
 	help
 	  This enables support for the ADMA (Advanced DMA) defined
 	  in the SD Host Controller Standard Specification Version 3.00 in SPL.