RISC-V: enable dynamic ftrace for RV32I

The RISC-V mcount function is now capable of supporting RV32I so make it
available in the kernel config.

Signed-off-by: Jamie Iles <jamie@jamieiles.com>
Link: https://lore.kernel.org/r/20221115200832.706370-5-jamie@jamieiles.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>