app: aboot: Disable fastboot commands registering for user builds

Disable registering fastboot commands for user builds by default.

Change-Id: I71056522bbe7545cfdd714763140443aa8872f8a
diff --git a/makefile b/makefile
index 0cf7e7c..1056726 100644
--- a/makefile
+++ b/makefile
@@ -60,6 +60,10 @@
   CFLAGS += -D_SIGNED_KERNEL=1
 endif
 
+ifeq ($(TARGET_BUILD_VARIANT),user)
+  CFLAGS += -DDISABLE_FASTBOOT_CMDS=1
+endif
+
 # setup toolchain prefix
 TOOLCHAIN_PREFIX ?= arm-eabi-
 CFLAGS += -fstack-protector-all