kbuild: xz_wrap: do not include include/config/auto.conf

Fix the following error:
./scripts/xz_wrap.sh: 315: include/config/auto.conf: Syntax error: "(" unexpected

Fixes: 83c382f436 ("FROMLIST: kbuild: Enable armthumb BCJ filter for Thumb-2 kernel")
Signed-off-by: Tao Huang <huangtao@rock-chips.com>
Change-Id: I780ac11132c7a42ad189fc9c955a94139a3d62aa

scripts/xz_wrap.sh

@@ -9,8 +9,6 @@
 # You can do whatever you want with this file.
 #
 
-. include/config/auto.conf
-
 BCJ=
 LZMA2OPTS=
 
@@ -22,7 +20,7 @@ case $SRCARCH in
 	sparc)          BCJ=--sparc ;;
 esac
 
-if [ -n "${CONFIG_THUMB2_KERNEL}" ]; then
+if grep -q "^CONFIG_THUMB2_KERNEL=y" include/config/auto.conf; then
 	BCJ=--armthumb
 fi