Documentation/features/vm: riscv supports THP now

After commit e88b333 ("riscv: mm: add THP support on 64-bit"),
riscv can support THP.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Link: https://lore.kernel.org/r/20210805002739.23f44d2d@xhacker
Signed-off-by: Jonathan Corbet <corbet@lwn.net>

Documentation/features/vm/THP/arch-support.txt

@@ -22,7 +22,7 @@
     |    openrisc: |  ..  |
     |      parisc: | TODO |
     |     powerpc: |  ok  |
-    |       riscv: | TODO |
+    |       riscv: |  ok  |
     |        s390: |  ok  |
     |          sh: |  ..  |
     |       sparc: |  ok  |