bsd dd: include prebuilt bsd dd in twrp for Nougat and greater

- Cleaned up toolbox/Android.mk so that BSD dd builds
  with correct Android versions

Change-Id: Idb15811480ec03b05336d54b866233b5ac99dfaf
diff --git a/prebuilt/Android.mk b/prebuilt/Android.mk
index e0e9dbc..05e750a 100644
--- a/prebuilt/Android.mk
+++ b/prebuilt/Android.mk
@@ -27,6 +27,9 @@
                                     if [ -e "$(TARGET_RECOVERY_ROOT_OUT)/sbin/fgrep" ]; then \
                                     rm $(TARGET_RECOVERY_ROOT_OUT)/sbin/fgrep; fi; ln -sr $(TARGET_RECOVERY_ROOT_OUT)/sbin/grep $(TARGET_RECOVERY_ROOT_OUT)/sbin/fgrep;
         RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/toybox
+        ifeq ($(shell test $(PLATFORM_SDK_VERSION) -gt 23; echo $$?),0)
+            RELINK_SOURCE_FILES += $(TARGET_RECOVERY_ROOT_OUT)/sbin/dd
+        endif
         ifneq ($(wildcard external/zip/Android.mk),)
             RELINK_SOURCE_FILES += $(TARGET_OUT_OPTIONAL_EXECUTABLES)/zip
         endif