Add i2c_interrupt_enable calls to enable interrupts

[hoverboardhavoc]

** NOT TESTED ON GD32F130C6 **

I ported this project to a split board. The board uses a GD32F130C8. I spent a lot of time trying to figure out why I2C0_EV_IRQHandler and I2C0_ER_IRQHandler were never called. The problem was that the i2c interrupts were never enabled.

    i2c_interrupt_enable(MPU_I2C, I2C_INT_ERR);
    i2c_interrupt_enable(MPU_I2C, I2C_INT_EV);
    i2c_interrupt_enable(MPU_I2C, I2C_INT_BUF);

I'm not sure why this project works on the GD32F130C6. Maybe the supporting libraries are subtly different or we're using different versions?

If this change does not break the GD32F130C6, I'd like you to merge to prevent other people wasting their time when trying to port the project

Thanks