Allow empty modules.load file to be generated

Currently, if BOARD_*_KERNEL_MODULES_LOAD is set to empty string, we
default to load all modules listed in BOARD_*_KERNEL_MODULES. For
system_dlkm, we do not want to load any modules unless they are
dependency of vendor kernel modules. Therefore we need to create an
empty modules.load file for system_dlkm. Add 'false' as an out of band
value to indicate that an empty modules.load file should be generated.

Bug: 149866755
Test: th
Change-Id: Ieaaeb2f9a824e97671acff465bbd4da83dfd9aa0
diff --git a/core/Makefile b/core/Makefile
index 80805f7..e96f210 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -447,6 +447,8 @@
 $(if $(strip $(BOARD_$(1)_KERNEL_MODULES$(_sep)$(_kver))$(BOARD_$(1)_KERNEL_MODULES_ARCHIVE$(_sep)$(_kver))),\
   $(if $(BOARD_$(1)_KERNEL_MODULES_LOAD$(_sep)$(_kver)),,\
     $(eval BOARD_$(1)_KERNEL_MODULES_LOAD$(_sep)$(_kver) := $(BOARD_$(1)_KERNEL_MODULES$(_sep)$(_kver)))) \
+  $(if $(filter false,$(BOARD_$(1)_KERNEL_MODULES_LOAD$(_sep)$(_kver))),\
+    $(eval BOARD_$(1)_KERNEL_MODULES_LOAD$(_sep)$(_kver) :=),) \
   $(call copy-many-files,$(call build-image-kernel-modules,$(BOARD_$(1)_KERNEL_MODULES$(_sep)$(_kver)),$(2),$(3),$(call intermediates-dir-for,PACKAGING,depmod_$(1)$(_sep)$(_kver)),$(BOARD_$(1)_KERNEL_MODULES_LOAD$(_sep)$(_kver)),$(4),$(BOARD_$(1)_KERNEL_MODULES_ARCHIVE$(_sep)$(_kver)),$(_stripped_staging_dir),$(_kver)))) \
 $(if $(_kver), \
   $(eval _dir := $(_kver)/), \