ash: factor out ASH_HELP config option

It used to be aliased to !FEATURE_SH_EXTRA_QUIET for ash,
while hush had it separate from FEATURE_SH_EXTRA_QUIET.

Bring ash in line with hush.

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
diff --git a/shell/ash.c b/shell/ash.c
index 4ead6f9..293f151 100644
--- a/shell/ash.c
+++ b/shell/ash.c
@@ -143,6 +143,13 @@
 //config:	help
 //config:	  Enable support for test builtin in ash.
 //config:
+//config:config ASH_HELP
+//config:	bool "help builtin"
+//config:	default y
+//config:	depends on ASH
+//config:	help
+//config:	  Enable help builtin in ash.
+//config:
 //config:config ASH_CMDCMD
 //config:	bool "'command' command to override shell builtins"
 //config:	default y
@@ -8804,8 +8811,8 @@
 		if (!did_banner) {
 			/* note: ash and hush share this string */
 			out1fmt("\n\n%s %s\n"
-				"Enter 'help' for a list of built-in commands."
-				"\n\n",
+				IF_ASH_HELP("Enter 'help' for a list of built-in commands.\n")
+				"\n",
 				bb_banner,
 				"built-in shell (ash)"
 			);
@@ -9058,7 +9065,7 @@
 #if ENABLE_ASH_GETOPTS
 static int getoptscmd(int, char **) FAST_FUNC;
 #endif
-#if !ENABLE_FEATURE_SH_EXTRA_QUIET
+#if ENABLE_ASH_HELP
 static int helpcmd(int, char **) FAST_FUNC;
 #endif
 #if MAX_HISTORY
@@ -9134,7 +9141,7 @@
 	{ BUILTIN_REGULAR       "getopts" , getoptscmd },
 #endif
 	{ BUILTIN_NOSPEC        "hash"    , hashcmd    },
-#if !ENABLE_FEATURE_SH_EXTRA_QUIET
+#if ENABLE_ASH_HELP
 	{ BUILTIN_NOSPEC        "help"    , helpcmd    },
 #endif
 #if MAX_HISTORY
@@ -12611,10 +12618,7 @@
 
 /* ============ Builtins */
 
-#if !ENABLE_FEATURE_SH_EXTRA_QUIET
-/*
- * Lists available builtins
- */
+#if ENABLE_ASH_HELP
 static int FAST_FUNC
 helpcmd(int argc UNUSED_PARAM, char **argv UNUSED_PARAM)
 {
@@ -12632,7 +12636,7 @@
 			col = 0;
 		}
 	}
-#if ENABLE_FEATURE_SH_STANDALONE
+# if ENABLE_FEATURE_SH_STANDALONE
 	{
 		const char *a = applet_names;
 		while (*a) {
@@ -12644,11 +12648,11 @@
 			a += strlen(a) + 1;
 		}
 	}
-#endif
+# endif
 	out1fmt("\n\n");
 	return EXIT_SUCCESS;
 }
-#endif /* FEATURE_SH_EXTRA_QUIET */
+#endif
 
 #if MAX_HISTORY
 static int FAST_FUNC