kbuild: make 'make help' show all *config targets and update descriptions slightly.

"make help" doesn't show "make randconfig" nor "make config" as options
and the description of oldconfig could be better (IMHO). Patch below adds
the missing targets to the help and updates the description of oldconfig.
Signed-off-by: Jesper Juhl <juhl-lkml@dif.dk>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>

scripts/kconfig/Makefile

@@ -50,10 +50,12 @@ endif
 
 # Help text used by make help
 help:
-	@echo  '  oldconfig	  - Update current config utilising a line-oriented program'
+	@echo  '  config	  - Update current config utilising a line-oriented program'
 	@echo  '  menuconfig	  - Update current config utilising a menu based program'
 	@echo  '  xconfig	  - Update current config utilising a QT based front-end'
 	@echo  '  gconfig	  - Update current config utilising a GTK based front-end'
+	@echo  '  oldconfig	  - Update current config utilising a provided .config as base'
+	@echo  '  randconfig	  - New config with random answer to all options'
 	@echo  '  defconfig	  - New config with default answer to all options'
 	@echo  '  allmodconfig	  - New config selecting modules when possible'
 	@echo  '  allyesconfig	  - New config where all options are accepted with yes'