uboot: (firmwareOdroidC2/C4) don't invoke patch tool, use patches = [] instead

https://github.com/NixOS/nixpkgs/blob/master/pkgs/stdenv/generic/setup.sh#L948
this can do it nicely.

Signed-off-by: Anton Arapov <anton@deadbeef.mx>

pkgs/build-support/fetchmtn/builder.sh

@@ -0,0 +1,51 @@
+source $stdenv/setup
+
+set -x
+
+if ! [ -f "$cacheDB" ]; then
+    echo "Creating cache DB $cacheDB"
+    mtn --db "$cacheDB" db init
+fi
+
+header "getting revision $selector";
+
+done=;
+for source in $dbs; do
+    if mtn pull --db "$cacheDB" "$source" "${branch}"; then
+        revision="$(mtn --db "$cacheDB" au toposort $(mtn --db "$cacheDB" au select "$selector") | tail -1)";
+        if [ -n "$revision" ]; then
+            if mtn --db "$cacheDB" au get_revision "$revision"; then
+                echo "found revision $revision"
+                done=1;
+            else
+                echo "revision $revision does not exist";
+            fi
+        else
+            echo "selector $selector does not match any revision";
+        fi
+    else
+        echo "pulling branch $branch wasn't successful";
+    fi;
+    if test -n "$done"; then
+        break;
+    fi;
+done;
+
+stopNest;
+
+header "checking out the revision $revision";
+
+if test -n "$done"; then
+    mtn checkout --db "$cacheDB" -r "$revision" "$out" -b "${branch}"
+else
+    echo "Needed revision still not found. Exiting";
+    exit 1;
+fi;
+
+stopNest
+
+header "clearing _MTN in the output"
+
+rm -rf "$out/_MTN"
+
+stopNest