ata: Migrate CONFIG_SCSI_AHCI to Kconfig

And use 'imply' liberally.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
diff --git a/configs/mvebu_db-88f3720_defconfig b/configs/mvebu_db-88f3720_defconfig
index 0fd4514..283a964 100644
--- a/configs/mvebu_db-88f3720_defconfig
+++ b/configs/mvebu_db-88f3720_defconfig
@@ -36,6 +36,7 @@
 CONFIG_ISO_PARTITION=y
 CONFIG_EFI_PARTITION=y
 CONFIG_ENV_IS_IN_SPI_FLASH=y
+CONFIG_SCSI_AHCI=y
 CONFIG_BLOCK_CACHE=y
 CONFIG_DM_GPIO=y
 # CONFIG_MVEBU_GPIO is not set