video: ARM CLCD: Fix DT-related build problems

This patch fixes the following error when !CONFIG_OF:

drivers/video/fbdev/amba-clcd.c:800:54: warning: ‘struct amba_dev’ declared inside parameter list [enabled by default]
 static struct clcd_board *clcdfb_of_get_board(struct amba_dev *dev)
                                                      ^
and adds a missing Kconfig select causing this
when CONFIG_OF && !CONFIG_FB_MODE_HELPERS:

drivers/video/fbdev/amba-clcd.c:567: undefined reference to `fb_videomode_from_videomode'

Reported-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>