RISC-V: Enable KVM in RV64 and RV32 defconfigs as a module

Let's enable KVM RISC-V in RV64 and RV32 defconfigs as module
so that it always built along with the default kernel image.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>