RISC-V: Avoid coupling the T-Head CMOs and Zicbom

We could make the T-Head CMOs depend on a new-enough assembler to have
Zicbom, but it's not strictly necessary because the T-Head CMOs
circumvent the assembler.

Fixes: 8f7e001e ("RISC-V: Clean up the Zicbom block size probing")
Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Conor Dooley <conor.dooley@microchip.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20220915170900.22685-1-palmer@rivosinc.com


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