Initial work for the mmc_disk driver

No read and write support for now. But we implement getting SD card
capacity. SDHC is not supported yet (it uses a different layout for the
CSD register which will be rejected by this version of the code)

Change-Id: Ife844a62f3846c0a780259e9a3a08195e2fd965e
Reviewed-on: https://review.haiku-os.org/c/haiku/+/1068
Reviewed-by: Jérôme Duval <[email protected]>

headers/private/drivers/mmc.h

@@ -1,5 +1,5 @@
 /*
- * Copyright 2019, Haiku, Inc. All Rights Reserved.
+ * Copyright 2019-2020, Haiku, Inc. All Rights Reserved.
  * Distributed under the terms of the MIT License.
  *
  * Authors:
@@ -25,7 +25,8 @@ enum {
 };
 
 
-// Interface between mmc_bus and underlying implementation
+// Interface between mmc_bus and underlying implementation (sdhci_pci or any
+// other thing that can execute mmc commands)
 typedef struct mmc_bus_interface {
 	driver_module_info info;
 
@@ -44,4 +45,9 @@ typedef struct mmc_device_interface {
 } mmc_device_interface;
 
 
+// Device attribute paths for the MMC device
+static const char* kMmcRcaAttribute = "mmc/rca";
+static const char* kMmcTypeAttribute = "mmc/type";
+
+
 #endif /* _MMC_H */