mm/hmm: allow HMM_MIRROR on all architectures with MMU

There isn't really any architecture specific code in this page table walk
implementation, so drop the dependencies.

Link: https://lore.kernel.org/r/20190806160554.14046-14-hch@lst.deSigned-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Jason Gunthorpe <jgg@mellanox.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

mm/Kconfig

@@ -677,8 +677,7 @@ config DEV_PAGEMAP_OPS
 
 config HMM_MIRROR
 	bool "HMM mirror CPU page table into a device page table"
-	depends on (X86_64 || PPC64)
-	depends on MMU && 64BIT
+	depends on MMU
 	select MMU_NOTIFIER
 	help
 	  Select HMM_MIRROR if you want to mirror range of the CPU page table of a