cmd: Add a memory-search command

It is useful to be able to find hex values and strings in a memory range.
Add a command to support this.

cmd: Fix 'md' and add a memory-search command
At present 'md.q' is broken. This series provides a fix for this. It also
implements a new memory-search command called 'ms'. It allows searching
memory for hex and string data.
END

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/README b/README
index 020918a..2384966 100644
--- a/README
+++ b/README
@@ -3237,6 +3237,7 @@
 mm	- memory modify (auto-incrementing)
 nm	- memory modify (constant address)
 mw	- memory write (fill)
+ms	- memory search
 cp	- memory copy
 cmp	- memory compare
 crc32	- checksum calculation
@@ -3482,6 +3483,15 @@
 		  CONFIG_NET_RETRY_COUNT, if defined. This value has
 		  precedence over the valu based on CONFIG_NET_RETRY_COUNT.
 
+  memmatches	- Number of matches found by the last 'ms' command, in hex
+
+  memaddr	- Address of the last match found by the 'ms' command, in hex,
+		  or 0 if none
+
+  mempos	- Index position of the last match found by the 'ms' command,
+		  in units of the size (.b, .w, .l) of the search
+
+
 The following image location variables contain the location of images
 used in booting. The "Image" column gives the role of the image and is
 not an environment variable name. The other columns are environment