ata: Migrate CONFIG_SCSI_AHCI to Kconfig

And use 'imply' liberally.

Signed-off-by: Tuomas Tynkkynen <tuomas.tynkkynen@iki.fi>
diff --git a/configs/qemu_arm_defconfig b/configs/qemu_arm_defconfig
index f353eea..3cd4d45 100644
--- a/configs/qemu_arm_defconfig
+++ b/configs/qemu_arm_defconfig
@@ -8,6 +8,7 @@
 CONFIG_CMD_PCI=y
 CONFIG_CMD_USB=y
 CONFIG_OF_BOARD=y
+CONFIG_SCSI_AHCI=y
 CONFIG_AHCI_PCI=y
 CONFIG_BLK=y
 # CONFIG_MMC is not set