watchdog: pnx4008_wdt: allow compile-testing

The only thing that prevents building this driver on other
platforms is the mach/hardware.h include, which is not actually
used here at all, so remove the line and allow CONFIG_COMPILE_TEST.

Acked-by: Sylvain Lemieux <slemieux.tyco@gmail.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Link: https://lore.kernel.org/r/20190809144043.476786-4-arnd@arndb.de


Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>