ACPI / platform: include missed header into acpi_platform.c

The internal.h declares the acpi_create_platform_device(). Without
that include we get a following warning:

drivers/acpi/acpi_platform.c:133:24: warning: symbol 'acpi_create_platform_device' was not declared. Should it be static?
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

drivers/acpi/acpi_platform.c

@@ -17,6 +17,8 @@
 #include <linux/module.h>
 #include <linux/platform_device.h>
 
+#include "internal.h"
+
 ACPI_MODULE_NAME("platform");
 
 /**