riscv: mm: hugetlb: Enable ARCH_WANT_HUGETLB_PAGE_OPTIMIZE_VMEMMAP

Add HVO support for RISC-V; see commit 6be24bed9da3 ("mm: hugetlb:
introduce a new config HUGETLB_PAGE_FREE_VMEMMAP"). This patch is
similar to commit 1e63ac088f20 ("arm64: mm: hugetlb: enable
HUGETLB_PAGE_FREE_VMEMMAP for arm64"), and riscv's motivation is the
same as arm64. The current riscv was ready to enable HVO after fixup,
ref commit d33deda095d3 ("riscv/mm: hugepage's PG_dcache_clean flag
is only set in head page").

See Documentation/mm/vmemmap_dedup.rst for more details.

The HugeTLB VmemmapvOptimization (HVO) defaults to off in Kconfig.

Here is the riscv test log:
cat /proc/sys/vm/hugetlb_optimize_vmemmap
echo 8 > /sys/kernel/mm/hugepages/hugepages-2048kB/nr_hugepages
mount -t hugetlbfs none test/ -o pagesize=2048k
<Try some simple hugetlb test in test dir, no problem found.>

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Signed-off-by: Guo Ren <guoren@kernel.org>
Link: https://lore.kernel.org/linux-riscv/1F5AF29D-708A-483B-A29F-CAEE6F554866@linux.dev/
Acked-by: Muchun Song <songmuchun@bytedance.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Link: https://lore.kernel.org/r/20230201015259.3222524-1-guoren@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

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