dma-direct: remove the cached_kernel_address hook

dma-direct now finds the kernel address for coherent allocations based
on the dma address, so the cached_kernel_address hooks is unused and
can be removed entirely.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>

include/linux/dma-noncoherent.h

@@ -109,6 +109,5 @@ static inline void arch_dma_prep_coherent(struct page *page, size_t size)
 #endif /* CONFIG_ARCH_HAS_DMA_PREP_COHERENT */
 
 void *uncached_kernel_address(void *addr);
-void *cached_kernel_address(void *addr);
 
 #endif /* _LINUX_DMA_NONCOHERENT_H */