Documentation/networking/caif: Update documentation

Update drawing and remove description of old features.
Add HSI and USB link layers to the drawing.

Reported-by: Joerg Reisenweber <joerg.reisenweber@stericssion.com>
Signed-off-by: Sjur Brændeland <sjur.brandeland@stericssion.com>
Signed-off-by: David S. Miller <davem@davemloft.net>