updater: Allow devices to suppress BLKDISCARD

* On some devices TRIM is disabled for security reasons. Don't fail
  flashing the ROM because discard isn't possible in this case.

Change-Id: I044619c3e0b01a496d967ef136501d0190240ad4
diff --git a/updater/Android.mk b/updater/Android.mk
index 3d25913..b695545 100644
--- a/updater/Android.mk
+++ b/updater/Android.mk
@@ -74,6 +74,10 @@
     -Wall \
     -Werror
 
+ifeq ($(BOARD_SUPPRESS_EMMC_WIPE),true)
+    LOCAL_CFLAGS += -DSUPPRESS_EMMC_WIPE
+endif
+
 LOCAL_EXPORT_C_INCLUDE_DIRS := \
     $(LOCAL_PATH)/include