platform/x86: silead_dmi: Add entry for Insyde 7W tablets

Add an entry providing the necessary info to make the touchscreen work
on various tablets based on the Insyde 7W whitebox tablet.

This has been tested on a DEXP Ursus 7W tablet.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>