kernel: Support switch branch or tag (#382)

kernel/setup.sh

@@ -18,7 +18,11 @@ fi
 test -d "$GKI_ROOT/KernelSU" || git clone https://github.com/tiann/KernelSU
 cd "$GKI_ROOT/KernelSU"
 git stash && git pull
-git checkout "$(git describe --abbrev=0 --tags)"
+if [ ! "$1" ]; then
+    git checkout "$(git describe --abbrev=0 --tags)"
+else
+    git checkout "$1"
+fi
 cd "$GKI_ROOT"
 
 echo "[+] GKI_ROOT: $GKI_ROOT"