atyfb: fix CONFIG_ namespace violations

Fix namespace violations by changing non-kconfig CONFIG_ names to CNFG_*.

Fixes breakage in staging/, which adds a real CONFIG_PANEL.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>