su: Introduce conditional for building

Do not build the standard su binary when FP2_USE_APPOPS_SU is set to
true. This mechanism allows for building of an alternative su binary,
for example to allow for superuser access by applications.

Issue: FP2P-458
Change-Id: Ib7eb0e4dba9cf89a80b8ade286369cfeca7492c0
diff --git a/su/Android.mk b/su/Android.mk
index 92ad5e3..392f66d 100644
--- a/su/Android.mk
+++ b/su/Android.mk
@@ -1,3 +1,4 @@
+ifneq ($(FP2_USE_APPOPS_SU),true)
 LOCAL_PATH:= $(call my-dir)
 include $(CLEAR_VARS)
 
@@ -11,3 +12,4 @@
 LOCAL_MODULE_TAGS := debug
 
 include $(BUILD_EXECUTABLE)
+endif