Add a command to read raw blocks from a partition

Sometimes data is on a block device and within a partition, but not in a
particular filesystem.

This commands permits reading raw data from a partition.

Signed-off-by: Kenneth Waters <kwaters@chromium.org>
Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/README b/README
index d1c60de..5810ced 100644
--- a/README
+++ b/README
@@ -861,6 +861,7 @@
 		CONFIG_CMD_PING		* send ICMP ECHO_REQUEST to network
 					  host
 		CONFIG_CMD_PORTIO	* Port I/O
+		CONFIG_CMD_READ		* Read raw data from partition
 		CONFIG_CMD_REGINFO	* Register dump
 		CONFIG_CMD_RUN		  run command in env variable
 		CONFIG_CMD_SAVES	* save S record dump