i2c: mpc: Interrupt driven transfer

The fsl-i2c controller will generate an interrupt after every byte
transferred. Make use of this interrupt to drive a state machine which
allows the next part of a transfer to happen as soon as the interrupt is
received. This is particularly helpful with SMBUS devices like the LM81
which will timeout if we take too long between bytes in a transfer.

Signed-off-by: Chris Packham <chris.packham@alliedtelesis.co.nz>
Signed-off-by: Wolfram Sang <wsa@kernel.org>