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
1 file changed