drm/gma500: add support for atom e6xx lpc lvds i2c

add gpio bitbanging i2c adapter on LPC device of atom e6xx
gpu chipset to access lvds EDID
tested on SECO QuadMo747-E6xx-EXTREME Qseven platform

Reviewed-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>
Signed-off-by: Jan Safrata <jan.nikitenko@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>