platform/x86: intel_scu_wdt: Move driver from arch/x86

The ACPI-enabled Intel MID platforms neither have WDAT table nor proper IDs
to instantiate watchdog device. In order to keep them working move the board
code from arch/x86 to drivers/platform/x86.

Note, the complete SFI support is going to be removed, that's why PDx86
has been chosen as a new home for it. This is the only device which needs
additional code so far.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Hans de Goede <hdegoede@redhat.com>
Acked-by: Linus Walleij <linus.walleij@linaro.org>