block/ps3: fix slow VRAM IO

The current PS3 VRAM driver uses msleep() to wait for completion of RSX
DMA transfers between system memory and VRAM.  Depending on the system
timing, the processing delay and overhead of this msleep() call can
significantly impact VRAM driver IO.

To avoid the condition, add a short duration (200 usec max) udelay()
polling loop before entering the msleep() polling loop.

Signed-off-by: Hideyuki Sasaki <xhide@rd.scei.sony.co.jp>
Signed-off-by: Geoff Levand <geoffrey.levand@am.sony.com>
Acked-by: Jim Paris <jim@jtan.com>
Cc: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>