kernel: include built-in module list

Add modules.builtin to the kernel package for improved handling of loadable
and builtin modules. As with other distros, this allows 'modprobe <module>'
to consistently return success for both loaded/built-in modules, a useful
feature for presence-testing.

Given OpenWrt's few built-in modules, this change and related kmodloader
support add ~1 KB to the compressed image size.

Using sch_fq_codel (builtin) and sch_cake (loadable) for example:

     root@OpenWrt:/# modprobe sch_fq_codel && echo SUCCESS || echo FAIL
     SUCCESS
     root@OpenWrt:/# modprobe sch_cake && echo SUCCESS || echo FAIL
     SUCCESS

     root@OpenWrt:/# rmmod sch_fq_codel
     module is builtin

Signed-off-by: Tony Ambardar <[email protected]>

package/kernel/linux/Makefile

@@ -58,7 +58,9 @@ define Package/kernel
 endef
 
 define Package/kernel/install
-  # nothing to do
+	$(INSTALL_DIR) $(1)/$(MODULES_SUBDIR)
+	$(INSTALL_DATA) $(LINUX_DIR)/modules.builtin $(1)/$(MODULES_SUBDIR)
+	$(SED) 's,.*/,,' $(1)/$(MODULES_SUBDIR)/modules.builtin
 endef
 
 define Package/kernel/extra_provides