RISC-V: Export kernel symbols for kvm

Export a few symbols used by kvm module. Without this, kvm cannot
be compiled as a module.

Signed-off-by: Atish Patra <atish.patra@wdc.com>
Signed-off-by: Anup Patel <anup.patel@wdc.com>
Acked-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Alexander Graf <graf@amazon.com>
[paul.walmsley@sifive.com: updated to apply; clarified short patch
 description]
Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>