mfd: intel-lpss: Add Intel Elkhart Lake PCH PCI IDs

Intel Elkhart Lake has the same LPSS than Intel Broxton.
Add the new IDs to the list of supported devices.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>