buildsystem: ensure directory exists before use

In some cases we request mktemp to create a temporary file in
$(obj)/mainboard/... before it exists.
Let's make sure the directory exists

Change-Id: I51f0065c30b1f25eb501a6fd5edefb3f4c15d0ab
Signed-off-by: Patrick Georgi <patrick.georgi@secunet.com>
Reviewed-on: http://review.coreboot.org/1532
Tested-by: build bot (Jenkins)
Reviewed-by: Marc Jones <marcj303@gmail.com>
diff --git a/Makefile.inc b/Makefile.inc
index 63c0403..1ba56b0 100644
--- a/Makefile.inc
+++ b/Makefile.inc
@@ -126,7 +126,7 @@
 			$(eval tmp-cbfs-file:= $($(2)-file))) \
 		$(if $(tmp-cbfs-method), \
 			$(eval tmp-old-cbfs-file:=$(tmp-cbfs-file)) \
-			$(eval tmp-cbfs-file:=$(shell mktemp $(obj)/mainboard/$(MAINBOARDDIR)/cbfs-file.XXXXXX).out) \
+			$(eval tmp-cbfs-file:=$(shell mkdir -p $(obj)/mainboard/$(MAINBOARDDIR); mktemp $(obj)/mainboard/$(MAINBOARDDIR)/cbfs-file.XXXXXX).out) \
 			$(call cbfs-files-processor-$(tmp-cbfs-method),$(tmp-old-cbfs-file),$(tmp-cbfs-file))) \
 		$(eval cbfs-files += $(tmp-cbfs-file)|$(2)|$($(2)-type)|$($(2)-compression)|$($(2)-position)) \
 		$(eval $(2)-name:=) \