sunxi: update SATA driver to always use DM_SCSI

It seems like the Allwinner SATA driver is already quite capable of
using the driver model, so we can force this on all boards and can
remove support for a non-DM_SCSI build.
This removes the warning about boards with SATA ports not being
DM_SCSI compliant.

It also takes the opportunity to move the driver out of the board/sunxi
directory to join its siblings in drivers/ata, and to make it a proper
Kconfig citizen.

The board defconfigs stay untouched.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Jagan Teki <jagan@openedev.com>
[jagan: select DM_SCSI separately]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
diff --git a/drivers/ata/Kconfig b/drivers/ata/Kconfig
index 7ebee75..4be5c63 100644
--- a/drivers/ata/Kconfig
+++ b/drivers/ata/Kconfig
@@ -101,6 +101,14 @@
 	help
 	  Enable this driver to support the SIL3114 SATA controllers.
 
+config SUNXI_AHCI
+	bool "Enable Allwinner SATA driver support"
+	depends on AHCI
+	default y if ARCH_SUNXI
+	help
+	  Enable this driver to support the SATA controllers found in the
+	  Allwinner A10, A20 and R40 SoCs.
+
 config AHCI_MVEBU
 	bool "Marvell EBU AHCI SATA support"
 	depends on ARCH_MVEBU