ata: Migrate CONFIG_SCSI_AHCI to Kconfig

And use 'imply' liberally.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
diff --git a/configs/Bananapi_M2_Ultra_defconfig b/configs/Bananapi_M2_Ultra_defconfig
index 4c2c05c..8083510 100644
--- a/configs/Bananapi_M2_Ultra_defconfig
+++ b/configs/Bananapi_M2_Ultra_defconfig
@@ -13,6 +13,7 @@
 CONFIG_SPL_I2C_SUPPORT=y
 # CONFIG_CMD_FLASH is not set
 # CONFIG_CMD_FPGA is not set
+CONFIG_SCSI_AHCI=y
 CONFIG_AXP_DLDO4_VOLT=2500
 CONFIG_AXP_ELDO3_VOLT=1200
 CONFIG_SCSI=y