board-specific prep recovery imagefix recovery size issue

Allow device config provide extra steps when preparing recovery
For example: have limited space in recovery partition and
need remove /sbin binaries that are not used in recovery mode

Bug: 30304868
Change-Id: I3890b635f4625e6e39d52ca326f92206641bbea7
diff --git a/core/Makefile b/core/Makefile
index a3bdc3a..e880ec7 100644
--- a/core/Makefile
+++ b/core/Makefile
@@ -980,6 +980,7 @@
   $(hide) cp $(RECOVERY_INSTALL_OTA_KEYS) $(TARGET_RECOVERY_ROOT_OUT)/res/keys
   $(hide) cat $(INSTALLED_DEFAULT_PROP_TARGET) $(recovery_build_prop) \
           > $(TARGET_RECOVERY_ROOT_OUT)/default.prop
+  $(BOARD_RECOVERY_IMAGE_PREPARE)
   $(if $(filter true,$(BOARD_BUILD_SYSTEM_ROOT_IMAGE)), \
     $(hide) mkdir -p $(TARGET_RECOVERY_ROOT_OUT)/system_root; \
             rm -rf $(TARGET_RECOVERY_ROOT_OUT)/system; \