Enable I2C slave clock stretch by default?

[reynoldsbd]

I am using the RP2040 as an I2C slave, but it took quite a bit of trial and error before I realized that clock stretching is not enabled by default.

Would it make sense to set IC_CON.RX_FIFO_FULL_HLD_CTRL to 1 by default as part of i2c_set_slave_mode?

[reynoldsbd]

To be clear, I'm happy to open a PR to make the change myself! I just wanted to touch base here first in case there's some specific reason for the current behavior.

[Wren6991]

I think this makes a lot of sense