pinctrl: pinconf-generic: Infer map type from DT property

With the new 'groups' property, the DT parser can infer the map type
from the fact whether 'pins' or 'groups' is used to specify the pin
group to work on.
To maintain backwards compatibitliy with current usage of the DT
binding, this is only done when an invalid map type is passed to the
parsing function.

Signed-off-by: Soren Brinkmann <soren.brinkmann@xilinx.com>
pinctrl: meson: some fixes