ahci: Add a disk-controller uclass

Add a uclass ID for a disk controller. This can be used by AHCI/SATA or
other controller types. There are no operations and no interface so far,
but it is possible to probe a SATA device.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/drivers/block/Makefile b/drivers/block/Makefile
index eb8bda9..5eb87e0 100644
--- a/drivers/block/Makefile
+++ b/drivers/block/Makefile
@@ -5,6 +5,7 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
+obj-$(CONFIG_DISK) += disk-uclass.o
 obj-$(CONFIG_SCSI_AHCI) += ahci.o
 obj-$(CONFIG_DWC_AHSATA) += dwc_ahsata.o
 obj-$(CONFIG_FSL_SATA) += fsl_sata.o