riscv: mm: mark CBO relate initialization funcs as __init

The two functions cbo_get_block_size() and riscv_init_cbo_blocksizes()
are only called during booting, mark them as __init.

Signed-off-by: Jisheng Zhang <jszhang@kernel.org>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20230614165504.532-3-jszhang@kernel.org


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