virtio-mem: Enable virtio-mem for RISC-V

Now that RISC-V has memory hotplugging support, virtio-mem can be used
on the platform.
Acked-by: David Hildenbrand <david@redhat.com>
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20240605114100.315918-10-bjorn@kernel.orgSigned-off-by: Palmer Dabbelt <palmer@rivosinc.com>

drivers/virtio/Kconfig

@@ -122,7 +122,7 @@ config VIRTIO_BALLOON
 
 config VIRTIO_MEM
 	tristate "Virtio mem driver"
-	depends on X86_64 || ARM64
+	depends on X86_64 || ARM64 || RISCV
 	depends on VIRTIO
 	depends on MEMORY_HOTPLUG
 	depends on MEMORY_HOTREMOVE