RISC-V: Enable profiling by default

Let us enable profiling by default in RV32 and RV64 defconfigs so
that we can use RISC-V PMU drivers on various RISC-V platforms.

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