Whitelist HAL FD for vr_window_manager.

A new API was added to gralloc that exposes this FD.

Bug: 32541196
Test: `m -j32` succeeds. Sailfish device boots.
Change-Id: I605e5ba826cdce1518e33649d3f787610db43aee

public/vr_wm.te

@@ -20,6 +20,9 @@ allow vr_wm system_file:dir r_dir_perms;
 allow vr_wm gpu_device:chr_file rw_file_perms;
 allow vr_wm ion_device:chr_file r_file_perms;
 
+# Get buffer metadata.
+allow vr_wm hal_graphics_allocator:fd use;
+
 use_pdx(vr_wm, bufferhubd)
 use_pdx(vr_wm, sensord)
 use_pdx(vr_wm, surfaceflinger)