ps3av: misc updates

ps3av:
  - Move the definition of struct ps3av to ps3av.c, as it's locally used only.
  - Kill ps3av.sem, use the existing ps3av.mutex instead.
  - Make the 512-byte buffer in ps3av_do_pkt() static to reduce stack usage.
    Its use is protected by a semaphore anyway.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>