platform/x86: x86-android-tablets: Move DMI match table into its own dmi.c file

In order to have a single MODULE_DEVICE_TABLE(dmi, ...), while allowing
splitting the board descriptions into multiple files, add a new separate
file for the DMI match table.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20230301092331.7038-5-hdegoede@redhat.com