Allow bufferhub service to allocate buffer

Test: build passed.
Bug: 118614333
Change-Id: I3b33d73a2cc7e78119de8b0913b4e2d0ac4a3235

private/fwk_bufferhub.te

 type fwk_bufferhub, domain, coredomain;
 type fwk_bufferhub_exec, system_file_type, exec_type, file_type;
 
+hal_client_domain(fwk_bufferhub, hal_graphics_allocator)
+allow fwk_bufferhub ion_device:chr_file r_file_perms;
+
 hal_server_domain(fwk_bufferhub, hal_bufferhub)
 init_daemon_domain(fwk_bufferhub)