FROMLIST: kbuild: install the modules.order for external modules

Add support to install the modules.order file for external modules
during module_install in order to retain the Makefile ordering
of external modules. This helps reduce the extra steps necessary to
properly order loading of external modules when there are multiple
kernel modules compiled within a given KBUILD_EXTMOD directory.

To handle compiling multiple external modules within the same
INSTALL_MOD_DIR, kbuild will append a suffix to the installed
modules.order file defined like so:

  echo "${KBUILD_EXTMOD}" | md5sum | cut -d " " -f 1

Example:
  KBUILD_EXTMOD=/mnt/a.b/c-d/my_driver results in:
  modules.order.7dd3eb90588c21ac15f23a96c2f6d8ec

The installed module.order.$(extmod_suffix) files can then be appended
to the staging modules.order file which defines the order to load all of
the modules during boot.

Example:
  cd $(MODLIB)
  find extra/. -name modules.order.* -exec cat {} >> modules.order \;

Link: https://lore.kernel.org/all/20220127010009.2617569-1-willmcvicker@google.com/
Bug: 216462633
Bug: 210713925
Signed-off-by: Will McVicker <willmcvicker@google.com>
Change-Id: I7baa92163f8e6ea3f47d780b728167d86cc2f6e1

scripts/Makefile.modinst

@@ -24,6 +24,10 @@ suffix-$(CONFIG_MODULE_COMPRESS_XZ)	:= .xz
 suffix-$(CONFIG_MODULE_COMPRESS_ZSTD)	:= .zst
 
 modules := $(patsubst $(extmod_prefix)%, $(dst)/%$(suffix-y), $(modules))
+ifneq ($(KBUILD_EXTMOD),)
+extmod_suffix := $(shell echo "${KBUILD_EXTMOD}" | md5sum | cut -d " " -f 1)
+modules += $(dst)/modules.order.$(extmod_suffix)
+endif
 
 __modinst: $(modules)
 	@:
@@ -82,6 +86,12 @@ $(dst)/%.ko: $(extmod_prefix)%.ko FORCE
 	$(call cmd,strip)
 	$(call cmd,sign)
 
+ifneq ($(KBUILD_EXTMOD),)
+$(dst)/modules.order.$(extmod_suffix): $(MODORDER) FORCE
+	$(call cmd,install)
+	@sed -i "s:^$(KBUILD_EXTMOD):$(INSTALL_MOD_DIR):g" $@
+endif
+
 else
 
 $(dst)/%.ko: FORCE