[POWERPC] PS3: Rework AV settings driver

Make the PS3 ps3av driver a loadable module.
  - Replace static data with kmalloc()'ed.
      o Allocate struct ps3av dynamically, as it contains data used as vuart
        receive/transmit buffers
      o Move static recv_buf from ps3av_do_pkt() to struct ps3av
  - Move ps3av_vuart_{read,write}() from drivers/ps3/ps3av_cmd.c to
    drivers/ps3/ps3av.c and make them static as they're used in that file only.
  - Make device a PS3 system-bus device.
  - Update copyright formatting.
  - Make two new routines ps3av_register_flip_ctl() and ps3av_flip_ctl() to
    support late binding of the frame buffer flip control routine.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>