mfd: lpc_ich: Separate device cells for clarity

The lpc_ich_cells array gives the wrong impression about the
relationship between the watchdog and GPIO devices. They are
completely distinct devices, so this patch separates the
array into distinct mfd_cell structs per device.

A side effect of removing the array, is that the lpc_cells enum
is no longer needed.

Signed-off-by: Aaron Sierra <asierra@xes-inc.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>