x86/platform/intel-mid: Remove unused header inclusion in intel-mid.h

After the commit f1be6cda ("x86/platform/intel-mid: Make
intel_scu_device_register() static") the platform_device.h is not being
used anymore by intel-mid.h. Remove it.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>