platform/x86: serdev_helpers: Add get_serdev_controller_from_parent() helper

platform/x86: serdev_helpers: Add get_serdev_controller_from_parent() helper

The x86-android-tablets code needs to be able to get a serdev_controller
device from a PCI parent, rather then by the ACPI HID+UID of the parent,
because on some tablets the UARTs are enumerated as PCI devices instead
of ACPI devices.

Split the code to walk the device hierarchy to find the serdev_controller
from its parents out into a get_serdev_controller_from_parent() helper
so that the x86-android-tablets code can re-use it.

Reviewed-by: Andy Shevchenko <andy@kernel.org>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20241204204227.95757-5-hdegoede@redhat.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>