Add support for Acer Aspire 7551.

Cc: Darren Hart <dvhart@infradead.org>
Cc: Andy Shevchenko <andy@infradead.org>
Signed-off-by: Peter Feuerer <peter@piie.net>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>