build: ensure PKG_INFO_DIR exists before trying to use it

PKG_INFO_DIR is only created at the finish step of the first package
build, but kernel modules now use it at the start. Doing a parallel build
could cause a kernel module to be the first package, breaking the build.

Fix this by ensuring the directory exists.

Fixes: 2e496876c6 ("kernel: collect module symvers for external modules")
Signed-off-by: Jonas Gorski <jonas.gorski@gmail.com>

include/kernel.mk

@@ -133,6 +133,7 @@ define populate_module_symvers
 endef
 
 define collect_module_symvers
+	@mkdir -p $(PKG_INFO_DIR)
 	for subdir in $(PKG_EXTMOD_SUBDIRS); do \
 		grep -F $(PKG_BUILD_DIR) $(PKG_BUILD_DIR)/$$$$subdir/Module.symvers >> $(PKG_BUILD_DIR)/Module.symvers.tmp; \
 	done; \