kbuild: modsign: read modules.order instead of $(MODVERDIR)/*.mod

Towards the goal of removing MODVERDIR, read out modules.order to get
the list of modules to be signed. This is simpler than parsing *.mod
files in $(MODVERDIR).

The modules_sign target is only supported for in-kernel modules.
So, this commit does not take care of external modules.
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

scripts/Makefile.modsign

@@ -8,8 +8,7 @@ __modsign:
 
 include scripts/Kbuild.include
 
-__modules := $(sort $(shell grep -h '\.ko$$' /dev/null $(wildcard $(MODVERDIR)/*.mod)))
-modules := $(patsubst %.o,%.ko,$(wildcard $(__modules:.ko=.o)))
+modules := $(sort $(shell cat modules.order))
 
 PHONY += $(modules)
 __modsign: $(modules)