serdev: Add serdev_device_id

Currently,a serdev device driver can only be used with devices that are
nodes of a device tree, or are part of the ACPI table.id_table will be
used for devices that are not part of the device tree nor the ACPI table
(example: device on greybus gbphy created uart).

corresponding modalias field is introduced to name the driver to be
used with the device, required device(s) that are neither described
by device tree nor ACPI table.

serdev_device_uevent is also extended for modalias devices.

Signed-off-by: Ricardo Ribalda Delgado <ricardo.ribalda@gmail.com>