platform/x86: Make SILEAD_DMI depend on TOUCHSCREEN_SILEAD

SILEAD_DMI provides platform specific data for the TOUCHSCREEN_SILEAD
driver. Make this explicitly clear in the Kconfig depends. Remove
INPUT as this is implied by TOUCHSCREEN_SILEAD.

Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Andy Shevchenko <andy@infradead.org>
Cc: Jean Delvare <jdelvare@suse.de>
Reviewed-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>