kbuild: Do not reference *-n variables in the Makefile

Kconfig options are either 'y', 'm', or undefined.
Signed-off-by: Michal Marek <mmarek@suse.cz>

Makefile

@@ -868,9 +868,7 @@ vmlinux-dirs	:= $(patsubst %/,%,$(filter %/, $(init-y) $(init-m) \
 		     $(net-y) $(net-m) $(libs-y) $(libs-m)))
 
 vmlinux-alldirs	:= $(sort $(vmlinux-dirs) $(patsubst %/,%,$(filter %/, \
-		     $(init-n) $(init-) \
-		     $(core-n) $(core-) $(drivers-n) $(drivers-) \
-		     $(net-n)  $(net-)  $(libs-n)    $(libs-))))
+		     $(init-) $(core-) $(drivers-) $(net-) $(libs-))))
 
 init-y		:= $(patsubst %/, %/built-in.o, $(init-y))
 core-y		:= $(patsubst %/, %/built-in.o, $(core-y))