cli: Enables using modern hush parser as command line parser

If one defines HUSH_MODERN_PARSER, it is then possible to use modern parser with:
=> cli get
old
=> cli set modern
=> cli get
modern

Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Francis Laniel <francis.laniel@amarulasolutions.com>

doc/usage/cmd/cli.rst

@@ -26,7 +26,7 @@ cli set
 
 It permits setting the value of the parser used by the CLI.
 
-Possible values are old and 2021.
+Possible values are old and modern.
 Note that, to use a specific parser its code should have been compiled, that
 is to say you need to enable the corresponding CONFIG_HUSH*.
 Otherwise, an error message is printed.
@@ -41,7 +41,14 @@ Get the current parser::
 
 Change the current parser::
 
+    => cli get
+    old
+    => cli set modern
+    => cli get
+    modern
     => cli set old
+    => cli get
+    old
 
 Trying to set the current parser to an unknown value::
 
@@ -51,7 +58,15 @@ Trying to set the current parser to an unknown value::
 
     Usage:
     cli get - print current cli
-    set - set the current cli, possible value is: old
+    set - set the current cli, possible values are: old, modern
+
+Trying to set the current parser to a correct value but its code was not
+compiled::
+
+    => cli get
+    modern
+    => cli set old
+    Want to set current parser to old, but its code was not compiled!
 
 Return value
 ------------