boards: atmel SAM: pinctrl fixes

Various boards are incorrectly specifying two pin control groups named
'group1' in the same parent node. Fix this by splitting them into two
groups, replacing redundant 'group1' with 'group2'.

Suggested-by: Gerson Fernando Budke <nandojve@gmail.com>
Signed-off-by: Martí Bolívar <marti.bolivar@nordicsemi.no>