[make] Add ability to deny modules from being used

Certain projects may want to prevent the usage of certain modules from
being used. Here are two examples of when this may occur:

1. The Project has it's own fdt library and does not want developer's
   using the version of libfdt included with LK

2. The project does not want developers using mincrypt.

`DENY_MODULES` is a list which developers can set in their own project
makefiles which is checked on each module inclusion. If that module is
on the deny list, it causes a build failure.

engine.mk

@@ -165,6 +165,9 @@ BUILDID ?=
 # comment out or override if you want to see the full output of each command
 NOECHO ?= @
 
+# Any modules you want to explictly prevent from being used
+DENY_MODULES :=
+
 # try to include the project file
 -include project/$(PROJECT).mk
 ifndef TARGET

make/module.mk

@@ -46,6 +46,10 @@ $(error MODULE $(MODULE) is probably setting OBJS, change to MODULE_SRCS)
 endif
 endif
 
+ifneq ($(filter $(MODULE),$(DENY_MODULES)),)
+$(error MODULE $(MODULE) is not allowed by PROJECT $(PROJECT)'s DENY_MODULES list)
+endif
+
 MODULE_SRCDIR := $(MODULE)
 MODULE_BUILDDIR := $(call TOBUILDDIR,$(MODULE_SRCDIR))