i2c: iproc: handle rx fifo full interrupt

Add code to handle IS_S_RX_FIFO_FULL_SHIFT interrupt to support
master write request with >= 64 bytes.

Iproc has a slave rx fifo size of 64 bytes.
Rx fifo full interrupt (IS_S_RX_FIFO_FULL_SHIFT) will be generated
when RX fifo becomes full. This can happen if master issues write
request of more than 64 bytes.

Signed-off-by: Rayagonda Kokatanur <rayagonda.kokatanur@broadcom.com>
Acked-by: Ray Jui <ray.jui@broadcom.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>