This commit adds the lowerhalf driver support for the I2C Slave.
While not currently ideal, it is compatible with the upperhalf i2c slave driver.
A workqueue can be used to delegate the isr work to the upperhalf driver.
But keep in mind wq introduces a lot of delay and in certain scenarios,
it is better to write your own better upperhalf driver.
Signed-off-by: Stepan Pressl <pressl.stepan@gmail.com>
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