Implements data_ready_en, fifo_overflow_en keys
Fixes i2c read bug, write will require similar changes
if needed for over 16 bytes. FIFO buffer size is only
16 bytes, hence flushing the buffer is required during
a transfer. See src/i2c/i2c_system.c for the wait function
and the src/i2c/i2c_read.c for an implementation example.