pinctrl: intel: Add support for variable size pad groups

The Intel GPIO hardware has a concept of pad groups, which means 1 to 32
pads occupying their own GPI_IS, GPI_IE, PAD_OWN and so on registers. The
existing hardware has the same amount of pads in each pad group (except the
last one) so it is possible to use community->gpp_size to calculate start
offset of each register.

With the next generation SoCs the pad group size is not always the same
anymore which means we cannot use community->gpp_size for register offset
calculations directly.

To support variable size pad groups we introduce struct intel_padgroup that
can be filled in by the client drivers according the hardware pad group
layout. The core driver will always use these when it performs calculations
for pad register offsets. The core driver will automatically populate pad
groups based on community->gpp_size if the driver does not provide any.
This makes sure the existing drivers still work as expected.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Chuah, Kim Tatt <kim.tatt.chuah@intel.com>
Signed-off-by: Tan Jui Nee <jui.nee.tan@intel.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>