platform/chrome: Centralize common cros_ec_device initialization

platform/chrome: Centralize common cros_ec_device initialization

Move the common initialization from protocol device drivers into central
cros_ec_device_alloc().

This removes duplicated code from each driver's probe function.
The buffer sizes are now calculated once, using the maximum possible
overhead required by any of the transport protocols, ensuring the
allocated buffers are sufficient for all cases.

Link: https://lore.kernel.org/r/20250828083601.856083-3-tzungbi@kernel.org
Signed-off-by: Tzung-Bi Shih <tzungbi@kernel.org>