ata: Migrate CONFIG_SCSI_AHCI to Kconfig

And use 'imply' liberally.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
diff --git a/configs/A20-OLinuXino-Lime2-eMMC_defconfig b/configs/A20-OLinuXino-Lime2-eMMC_defconfig
index cd1fa64..97f2e7d 100644
--- a/configs/A20-OLinuXino-Lime2-eMMC_defconfig
+++ b/configs/A20-OLinuXino-Lime2-eMMC_defconfig
@@ -21,6 +21,7 @@
 # CONFIG_SPL_DOS_PARTITION is not set
 # CONFIG_SPL_ISO_PARTITION is not set
 # CONFIG_SPL_PARTITION_UUIDS is not set
+CONFIG_SCSI_AHCI=y
 CONFIG_DFU_RAM=y
 CONFIG_ETH_DESIGNWARE=y
 CONFIG_RGMII=y