kbuild: move cmd_mkimage to scripts/Makefile.lib

Because cmd_mkimage is used in various subdirectories,
it seems reasonable to define it in scripts/Makefile.lib.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
diff --git a/board/cray/L1/Makefile b/board/cray/L1/Makefile
index 5540298..716a5a3 100644
--- a/board/cray/L1/Makefile
+++ b/board/cray/L1/Makefile
@@ -15,13 +15,9 @@
 $(obj)/bootscript.c: $(obj)/bootscript.image $(src)/x2c.awk
 	$(call cmd,awk)
 
-quiet_cmd_mkimage = MKIMAGE $@
-cmd_mkimage = $(objtree)/tools/mkimage $(MKIMAGEFLAGS_$(@F)) -d $< $@ \
-        $(if $(KBUILD_VERBOSE:1=), >/dev/null)
-
 MKIMAGEFLAGS_bootscript.image := -A ppc -O linux -T script -C none \
 						-a 0 -e 0 -n bootscript
 $(obj)/bootscript.image: $(src)/bootscript.hush
 	$(call cmd,mkimage)
 
-clean-files := bootscript.c bootscript.image
\ No newline at end of file
+clean-files := bootscript.c bootscript.image
diff --git a/board/matrix_vision/mvblm7/Makefile b/board/matrix_vision/mvblm7/Makefile
index 9ed2837..caa6cfd 100644
--- a/board/matrix_vision/mvblm7/Makefile
+++ b/board/matrix_vision/mvblm7/Makefile
@@ -8,10 +8,6 @@
 
 extra-y := bootscript.img
 
-quiet_cmd_mkimage = MKIMAGE $@
-cmd_mkimage = $(objtree)/tools/mkimage $(MKIMAGEFLAGS_$(@F)) -d $< $@ \
-        $(if $(KBUILD_VERBOSE:1=), >/dev/null)
-
 MKIMAGEFLAGS_bootscript.image := -T script -C none -n M7_script
 
 $(obj)/bootscript.img: $(src)/bootscript
diff --git a/board/matrix_vision/mvsmr/Makefile b/board/matrix_vision/mvsmr/Makefile
index a9c794e..cef1b76 100644
--- a/board/matrix_vision/mvsmr/Makefile
+++ b/board/matrix_vision/mvsmr/Makefile
@@ -12,10 +12,6 @@
 
 extra-y := bootscript.img
 
-quiet_cmd_mkimage = MKIMAGE $@
-cmd_mkimage = $(objtree)/tools/mkimage $(MKIMAGEFLAGS_$(@F)) -d $< $@ \
-        $(if $(KBUILD_VERBOSE:1=), >/dev/null)
-
 MKIMAGEFLAGS_bootscript.image := -T script -C none -n mvSMR_Script
 
 $(obj)/bootscript.img: $(src)/bootscript