treewide: fix GPLv2+ obsolete-license warnings

The LICENSE string 'GPLv2+' is considered obsolete by Yocto and raises a
warning.  Switch them too the accepted tag 'GPL-2.0-or-later'.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I88c639dbb45762e2e019a3503f1f1930b65c09d6
diff --git a/meta-nuvoton/recipes-bsp/u-boot/u-boot-common-nuvoton.inc b/meta-nuvoton/recipes-bsp/u-boot/u-boot-common-nuvoton.inc
index 7d605ae..f296955 100644
--- a/meta-nuvoton/recipes-bsp/u-boot/u-boot-common-nuvoton.inc
+++ b/meta-nuvoton/recipes-bsp/u-boot/u-boot-common-nuvoton.inc
@@ -2,7 +2,7 @@
 SECTION = "bootloaders"
 DEPENDS += "flex-native bison-native"
 
-LICENSE = "GPLv2+"
+LICENSE = "GPL-2.0-or-later"
 LIC_FILES_CHKSUM = "file://Licenses/README;md5=30503fd321432fc713238f582193b78e"
 
 UBRANCH = "npcm7xx-v2019.01"