build: pass KBUILD_EXTRA_SYMBOLS with symvers files for kernel module packages

This replaces the previous (deprecated) method of collecting symvers data
in $(PKG_BUILD_DIR)/Module.symvers, which does not work on newer kernels

Signed-off-by: Felix Fietkau <nbd@nbd.name>

include/kernel-build.mk

@@ -136,6 +136,7 @@ define BuildKernel
   $(LINUX_DIR)/.modules: export PKG_CONFIG_LIBDIR=$$(STAGING_DIR_HOST)/lib/pkgconfig
   $(LINUX_DIR)/.modules: $(STAMP_CONFIGURED) $(LINUX_DIR)/.config FORCE
 	$(Kernel/CompileModules)
+	mkdir -p $(PKG_SYMVERS_DIR)
 	touch $$@
 
   $(LINUX_DIR)/.image: export STAGING_PREFIX=$$(STAGING_DIR_HOST)