platform/x86: x86-android-tablets: Add an init() callback to struct x86_dev_info

Add an init() callback to struct x86_dev_info, board descriptions can use
this to do some custom setup before registering the i2c_clients, platform-
devices and servdevs.

Also add an exit() callback to also allow for cleanup of the custom setup.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-By: Lubomir Rintel <lkundrak@V3.sk>
Link: https://lore.kernel.org/r/20220110103952.48760-2-hdegoede@redhat.com