pinctrl: intel: Split intel_pinctrl_add_padgroups() for better maintenance

Currently the intel_pinctrl_add_padgroups() is twisted a bit due to
a different nature of the pin control hardware implementations. Thus,
its maintenance is a bit hard. Besides that some pieces of code
are run on all hardware and make this code slightly inefficient,
and moreover, validation for one case is done in a wrong time in a flow
which makes it even slower.

Split intel_pinctrl_add_padgroups() to two functions, one per hardware
implementation, for better maintenance and readability.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>