cmd: Update the memory-search command

Add various fixes and improvements to this command that were missed in
the original version. Unfortunately I forgot to send v2.

- Fix Kconfig name
- Use a separate variable for the remaining search length
- Correct a minor bug
- Move into a separate test suite
- Add -q flag to the 'quiet' test to test operation when console is enabled
- Enable the feature for sandbox

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index e111764..6ac274e 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -724,7 +724,7 @@
 	    base - print or set address offset
 	    loop - initialize loop on address range
 
-config MEM_SEARCH
+config CMD_MEM_SEARCH
 	bool "ms - Memory search"
 	help
 	  Memory-search command