kbuild: add dependency on kernel.release to the package targets

The binrpm-pkg target uses KERNELRELEASE when generated its .spec file.
When binrpm-pkg was the first build target run in a tree it generated the
.spec before kernel.release so the Version: tag in the .spec was empty.

I don't know if this is the best fix, but binrpm-pkg works when we
explicitly build kernel.release before descending into package-dir.

Signed-off-by: Zach Brown <[e-mail]>
Signed-off-by: Andrew Morton <[e-mail]>
Signed-off-by: Sam Ravnborg <[e-mail]>

Makefile

···
 # rpm target kept for backward compatibility
 package-dir	:= $(srctree)/scripts/package
 
-%pkg: FORCE
+%pkg: include/config/kernel.release FORCE
 	$(Q)$(MAKE) $(build)=$(package-dir) $@
-rpm: FORCE
+rpm: include/config/kernel.release FORCE
 	$(Q)$(MAKE) $(build)=$(package-dir) $@