dt-overlays: Use bitbake variable for lib directory

Required since use of usrmerge that make /lib a symlink to
/usr/lib

recipes-kernel/dt-overlays/dt-overlays.bb

@@ -21,7 +21,7 @@ dtos = " \
 
 
 
-FILES_${PN} += "/lib/firmware"
+FILES_${PN} += "${nonarch_base_libdir}/firmware"
 
 do_compile() {
     for dto in ${dtos}; do
@@ -30,8 +30,8 @@ do_compile() {
 }
 
 do_install() {
-    install -d ${D}/lib/firmware/
+    install -d ${D}${nonarch_base_libdir}/firmware/
     for dto in ${dtos}; do
-        install -m 0644 $dto.dtbo ${D}/lib/firmware/
+        install -m 0644 $dto.dtbo ${D}${nonarch_base_libdir}/firmware/
     done
 }