ps3fb: Tear down FB setup during cleanup

During cleanup, use L1GPU_CONTEXT_ATTRIBUTE_FB_CLOSE to tear down the setup
done by L1GPU_CONTEXT_ATTRIBUTE_FB_SETUP.

This allows unloading and reloading of ps3fb while the sound driver keeps the
GPU open.

Signed-off-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Cc: linux-fbdev-devel@lists.sourceforge.net
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>