target: add a feature flag for RTC support

git-svn-id: svn://svn.openwrt.org/openwrt/trunk@31777 3c298f89-4303-0410-b956-a3cf2f4a3e73

include/target.mk

@@ -183,6 +183,9 @@ ifeq ($(DUMP),1)
     ifneq ($(CONFIG_VGA_CONSOLE)$(CONFIG_FB),)
       FEATURES += display
     endif
+    ifneq ($(CONFIG_RTC_CLASS),)
+      FEATURES += rtc
+    endif
 
     # remove duplicates
     FEATURES:=$(sort $(FEATURES))