Convert CONFIG_CMDLINE_PS_SUPPORT to Kconfig

This converts the following to Kconfig:
   CONFIG_CMDLINE_PS_SUPPORT

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/cmd/Kconfig b/cmd/Kconfig
index c5eb71c..d3abe3a 100644
--- a/cmd/Kconfig
+++ b/cmd/Kconfig
@@ -31,6 +31,13 @@
 	  Enable editing and History functions for interactive command line
 	  input operations
 
+config CMDLINE_PS_SUPPORT
+	bool "Enable support for changing the command prompt string at run-time"
+	depends on HUSH_PARSER
+	help
+	  Only static string in the prompt is supported so far.  The string is
+	  obtained from environment variables PS1 and PS2.
+
 config AUTO_COMPLETE
 	bool "Enable auto complete using TAB"
 	depends on CMDLINE