combine block device load commands into common function

All the raw block load commands duplicate the same code. Starting with
the ide version as it has progress updates convert ide, usb, and scsi boot
commands to all use a common version.

Signed-off-by: Rob Herring <rob.herring@calxeda.com>

include/command.h

@@ -110,6 +110,10 @@ static inline int bootm_maybe_autostart(cmd_tbl_t *cmdtp, const char *cmd)
 	return 0;
 }
 #endif
+
+extern int common_diskboot(cmd_tbl_t *cmdtp, const char *intf, int argc,
+			   char *const argv[]);
+
 extern int do_reset(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[]);
 
 /*