arch: switch the default on ARCH_HAS_SG_CHAIN

These days architectures are mostly out of the business of dealing with
struct scatterlist at all, unless they have architecture specific iommu
drivers.  Replace the ARCH_HAS_SG_CHAIN symbol with a ARCH_NO_SG_CHAIN
one only enabled for architectures with horrible legacy iommu drivers
like alpha and parisc, and conditionally for arm which wants to keep it
disable for legacy platforms.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Palmer Dabbelt <palmer@sifive.com>
diff --git a/lib/Kconfig b/lib/Kconfig
index a9965f4..d5a5e2e 100644
--- a/lib/Kconfig
+++ b/lib/Kconfig
@@ -577,7 +577,7 @@
 # sg chaining option
 #
 
-config ARCH_HAS_SG_CHAIN
+config ARCH_NO_SG_CHAIN
 	def_bool n
 
 config ARCH_HAS_PMEM_API