avr32: Allow fine-grained control over LCDC pins

This replaces the pin_config param with an u64 pin_mask in
at32_add_device_lcdc, allowing a board-maintainer to indivually select
specific lcdc pins.

Signed-off-by: Alex Raimondi <raimondi@miromico.ch>
Signed-off-by: Julien May <jmay@miromico.ch>
Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>