module/pinctrl: Change set/get configuration for group

Make changes in set/get configuration regarding the change in the requirement analysis
to prevent set/get configuration if the group has more than one pin and is not GPIO.

Make a small change in the get_function_attributes to match the change in the group functionality
which allows every group to be linked to one and only one function.

Signed-off-by: Khaled Ali Ahmed <khaled.aliahmed@arm.com>