Disable xtest 20000 (FS corruption tests) when OP-TEE uses RPMB

When the filesystem is implemented over RPMB (CFG_RPMB_FS=y), there is
not point trying to corrupt files in the REE.

Signed-off-by: Jerome Forissier <jerome.forissier@linaro.org>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Reviewed-by: Pascal Brand <pascal.brand@linaro.org>
diff --git a/Android.mk b/Android.mk
index 33d03e5..b8c6bba 100644
--- a/Android.mk
+++ b/Android.mk
@@ -57,6 +57,9 @@
 ifeq ($(CFG_ENC_FS),y)
 LOCAL_CFLAGS += -DCFG_ENC_FS
 endif
+ifeq ($(CFG_RPMB_FS),y)
+LOCAL_CFLAGS += -DCFG_RPMB_FS
+endif
 
 LOCAL_CFLAGS += -DUSER_SPACE
 LOCAL_CFLAGS += -DTA_DIR=\"/system/lib/optee_armtz\"