imx6sl-evk, imx6sll-evk and imx6sx-sdb boards use a Seiko 43WVF1G panel.

Now that the DRM mxsfb driver is the one selected by default, let's
also select CONFIG_DRM_PANEL_SEIKO_43WVF1G so that these boards continue
to have a working display by default.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>