Allow system_server binder_call into hal_graphics_allocator

Test: no log spam for graphics allocator
Test: dmesg | audit2allow does not show denial for
hal_graphics_allocator_default
Test: system is responsive after boot (because
      android.hardware.graphics.allocator@2.0::IAllocator getService()
      will not be blocked)

Bug: 36220026
Change-Id: I3e103f88988fe4a94888e92ee8c5b1f27845ad9e