mlxcx_put32
extern void mlxcx_put32(mlxcx_t *, uintptr_t, uint32_t);
mlxcx_put32(mlxp, MLXCX_ISS_CMD_HIGH, cmd_high);
mlxcx_put32(mlxp, MLXCX_ISS_CMD_LOW, cmd_low);
mlxcx_put32(mlxp, MLXCX_ISS_CMD_DOORBELL, 1 << slot);