Separate aidl dependencies from compiler dependencies

Both aidl and clang/gcc were putting their dependencies in the same
place.  Move aidl's dependencies to a file ending with .aidl.P rather
than the compiler's .P.

While here, inform kati that we have these special dep files.

Bug:26409006
Test: Rebuild, note both files being generated

Change-Id: I29d2eea822235d60713c2059f3a314e475eb5aa3
diff --git a/core/definitions.mk b/core/definitions.mk
index 4b820de..916dfa2 100644
--- a/core/definitions.mk
+++ b/core/definitions.mk
@@ -989,7 +989,7 @@
 @mkdir -p $(dir $@)
 @mkdir -p $(PRIVATE_HEADER_OUTPUT_DIR)
 @echo "Generating C++ from AIDL: $(PRIVATE_MODULE) <= $<"
-$(hide) $(AIDL_CPP) -d$(basename $@).P $(PRIVATE_AIDL_FLAGS) \
+$(hide) $(AIDL_CPP) -d$(basename $@).aidl.P $(PRIVATE_AIDL_FLAGS) \
     $< $(PRIVATE_HEADER_OUTPUT_DIR) $@
 endef