treewide: Change .*GPL.*+ licenses to SPDX compatible identifier

The CONTRIBUTING.md requests an (or multiple) SPDX identifier for GPL
licenses. But a lot of packages did use a different, non-SPDX style with a
"+" at the end instead of "-or-later".

Signed-off-by: Sven Eckelmann <sven@narfation.org>

Makefile

@@ -8,9 +8,9 @@
 include $(TOPDIR)/rules.mk
 
 PKG_NAME:=cgi-io
-PKG_RELEASE:=7
+PKG_RELEASE:=8
 
-PKG_LICENSE:=GPL-2.0+
+PKG_LICENSE:=GPL-2.0-or-later
 
 PKG_MAINTAINER:=John Crispin <blogic@openwrt.org>