platform/surface: aggregator: Add error injection capabilities

This commit adds error injection hooks to the Surface Serial Hub
communication protocol implementation, to:

 - simulate simple serial transmission errors,

 - drop packets, requests, and responses, simulating communication
   failures and potentially trigger retransmission timeouts, as well as

 - inject invalid data into submitted and received packets.

Together with the trace points introduced in the previous commit, these
facilities are intended to aid in testing, validation, and debugging of
the Surface Aggregator communication layer.

Signed-off-by: Maximilian Luz <luzmaximilian@gmail.com>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Steven Rostedt (VMware) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20201221183959.1186143-6-luzmaximilian@gmail.com
Signed-off-by: Hans de Goede <hdegoede@redhat.com>