x86/mm: unencrypted non-blocking DMA allocations use coherent pools

When CONFIG_AMD_MEM_ENCRYPT is enabled and a device requires unencrypted
DMA, all non-blocking allocations must originate from the atomic DMA
coherent pools.

Select CONFIG_DMA_COHERENT_POOL for CONFIG_AMD_MEM_ENCRYPT.
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

arch/x86/Kconfig

@@ -1520,6 +1520,7 @@ config X86_CPA_STATISTICS
 config AMD_MEM_ENCRYPT
 	bool "AMD Secure Memory Encryption (SME) support"
 	depends on X86_64 && CPU_SUP_AMD
+	select DMA_COHERENT_POOL
 	select DYNAMIC_PHYSICAL_MASK
 	select ARCH_USE_MEMREMAP_PROT
 	select ARCH_HAS_FORCE_DMA_UNENCRYPTED