riscv: add support for hugepage migration

Generic arch_hugetlb_migration_supported can provide appropriate
support for hugepage migration when enable ARCH_ENABLE_HUGEPAGE_MIGRATION,
so enable it for hugepage migration in riscv.
Signed-off-by: NChen Wandun <chenwandun@huawei.com>
Signed-off-by: NPalmer Dabbelt <palmerdabbelt@google.com>

arch/riscv/Kconfig

@@ -13,6 +13,7 @@ config 32BIT
 config RISCV
 	def_bool y
 	select ARCH_CLOCKSOURCE_INIT
+	select ARCH_ENABLE_HUGEPAGE_MIGRATION if HUGETLB_PAGE && MIGRATION
 	select ARCH_HAS_BINFMT_FLAT
 	select ARCH_HAS_DEBUG_VM_PGTABLE
 	select ARCH_HAS_DEBUG_VIRTUAL if MMU