powerpc: Do not redefine NEED_DMA_MAP_STATE

kernel/dma/Kconfig already defines NEED_DMA_MAP_STATE, just select it
from CONFIG_PPC using the same condition as an if guard.

Signed-off-by: Christoph Hellwig <hch@lst.de>
[mpe: Move it under PPC]
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>