kconfig: environment symbol support

Add the possibility to import a value from the environment into kconfig
via the option syntax. Beside flexibility this has the advantage
providing proper dependencies.
Documented the options syntax.

Signed-off-by: Roman Zippel <zippel@linux-m68k.org>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
diff --git a/scripts/kconfig/qconf.cc b/scripts/kconfig/qconf.cc
index 9fe27ca..5d0fd38 100644
--- a/scripts/kconfig/qconf.cc
+++ b/scripts/kconfig/qconf.cc
@@ -1088,7 +1088,11 @@
 			debug += "</a><br>";
 			break;
 		case P_DEFAULT:
-			debug += "default: ";
+		case P_SELECT:
+		case P_RANGE:
+		case P_ENV:
+			debug += prop_get_type_name(prop->type);
+			debug += ": ";
 			expr_print(prop->expr, expr_print_help, &debug, E_NONE);
 			debug += "<br>";
 			break;
@@ -1099,16 +1103,6 @@
 				debug += "<br>";
 			}
 			break;
-		case P_SELECT:
-			debug += "select: ";
-			expr_print(prop->expr, expr_print_help, &debug, E_NONE);
-			debug += "<br>";
-			break;
-		case P_RANGE:
-			debug += "range: ";
-			expr_print(prop->expr, expr_print_help, &debug, E_NONE);
-			debug += "<br>";
-			break;
 		default:
 			debug += "unknown property: ";
 			debug += prop_get_type_name(prop->type);