i2c: Add helpers and context for i2c rtio drivers

Implementing RTIO drivers, in theory, should be as simple as the normal
i2c drivers and generally be more consistent across implementations. To
do that some common code that calls driver specific code is needed much
like the venerable spi_context and its helpers.

This adds struct i2c_rtio as well as helpers to perform blocking i2c
transfers, i2c bus recovery, and similar such tasks.

Signed-off-by: Tom Burdick <thomas.burdick@intel.com>