dma-direct: add dependencies to CONFIG_DMA_GLOBAL_POOL

CONFIG_DMA_GLOBAL_POOL can't be combined with other DMA coherent
allocators.  Add dependencies to Kconfig to document this, and make
kconfig complain about unmet dependencies if someone tries.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Robin Murphy <robin.murphy@arm.com>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Reviewed-by: Greg Ungerer <gerg@linux-m68k.org>
Tested-by: Greg Ungerer <gerg@linux-m68k.org>

kernel/dma/Kconfig

@@ -135,6 +135,8 @@ config DMA_COHERENT_POOL
 
 config DMA_GLOBAL_POOL
 	select DMA_DECLARE_COHERENT
+	depends on !ARCH_HAS_DMA_SET_UNCACHED
+	depends on !DMA_DIRECT_REMAP
 	bool
 
 config DMA_DIRECT_REMAP