platform/x86: silead_dmi: Add touchscreen info for Surftab Wintron 7.0

Add touchscreen info for the Trekstor Surftab Wintron 7.0 ST70416-6
tablet.

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