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>
diff --git a/common/Makefile b/common/Makefile
index 22e8a6f..482795e 100644
--- a/common/Makefile
+++ b/common/Makefile
@@ -34,6 +34,7 @@
 COBJS-y += s_record.o
 COBJS-$(CONFIG_SERIAL_MULTI) += serial.o
 COBJS-y += xyzModem.o
+COBJS-y += cmd_disk.o
 
 # core command
 COBJS-y += cmd_boot.o