SF: Move SurfaceFlingerFactory.cpp out of the filegroup

Having it in the sources for the binary makes it impossible to customize
the factories used when specializing SurfaceFlinger for a target.

Bug: 168284592
Test: build, boot bertha target
Change-Id: I22dbbf0ba5c56b8643eec35f24bffa7c4e55a52c
diff --git a/services/surfaceflinger/Android.bp b/services/surfaceflinger/Android.bp
index b017ad7..cf46e03 100644
--- a/services/surfaceflinger/Android.bp
+++ b/services/surfaceflinger/Android.bp
@@ -233,10 +233,7 @@
     name: "surfaceflinger_binary_sources",
     srcs: [
         ":libsurfaceflinger_sources",
-        // Note: SurfaceFlingerFactory is not in the default sources so that it
-        // can be easily replaced.
-        "SurfaceFlingerFactory.cpp",
-        "main_surfaceflinger.cpp"
+        "main_surfaceflinger.cpp",
     ],
 }
 
@@ -244,7 +241,12 @@
     name: "surfaceflinger",
     defaults: ["libsurfaceflinger_binary"],
     init_rc: ["surfaceflinger.rc"],
-    srcs: [":surfaceflinger_binary_sources"],
+    srcs: [
+        ":surfaceflinger_binary_sources",
+        // Note: SurfaceFlingerFactory is not in the filegroup so that it
+        // can be easily replaced.
+        "SurfaceFlingerFactory.cpp",
+    ],
     shared_libs: [
         "libSurfaceFlingerProp",
     ],