mpu i2c with cratus giving nak after start
MPU i2C Interrupt mode working now.
changed MPU init so interrupts will not be processed until after DMU is initialized.

**BUG**  When MPU triggers an interrupt, the ISR for port 1.7 is called and in that ISR it is trying to read the MPU data.  In order to read the MPU data, it is using the cratus I2C drivers which relies on i2c isr to send and receive bytes through the bus.  Since we are in the ISR routine for port1.7, the isr for i2c is not being processed.  This causes the i2c operations to timeout, thus we get no data.

To fix this either we can never call the i2c read through the mpu callback, or we can change our i2c driver back to ayantra method relying on polling.