atmel_lcdfb: Straighten out funky vl_sync logic

If the board _didn't_ request INVLINE_INVERTED, we set INVLINE_INVERTED,
otherwise we don't. WTF?

Signed-off-by: Haavard Skinnemoen <haavard.skinnemoen@atmel.com>
Signed-off-by: Anatolij Gustschin <agust@denx.de>