thunderbolt: Move driver ready handling to struct icm

Intel Titan Ridge uses slightly different format for ICM driver ready
response, so add a new ->driver_ready() callback to struct icm and move
the existing handling to a separate function which we then use in Falcon
Ridge and Alpine Ridge.

No functional changes intended.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>