I2C: Clear error bit on bus error, add STATUS_BYTE and STATUS_CML

When a bus error happened, the I2C peripheral's error bit remained
set. This caused it to respond erroneously in future transactions.

Now, when a bus error occurs, we're clearing the error bit and setting
the error flags in the STATUS_BYTE and STATUS_CML PMBus registers.
After the user reads those registers (using commands 0x78 and 0x7E),
their error flags are cleared.