i2c: add support for 10bit slave addresses

Slave addresses can be of 7bit or 10bit type, which occupies one or two
bytes at the start of the frame. Detect when a 10bit address is seen,
and classify the following byte as yet another address byte (which the
previous implementation incorrectly classified as data byte).

This commit only accumulates the address value and adjusts the class of
annotations. It does not introduce new annotation classes or rows, to
not change the decoder in incompatible ways.