Nokia RX-51: Convert to CONFIG_DM_VIDEO

Mechanically convert video_hw_init() function to UCLASS_VIDEO probe
callback and replace CONFIG_CFB_CONSOLE by CONFIG_DM_VIDEO.

As framebuffer base address is setup by the bootloader which loads U-Boot,
set plat->base to that fixed framebuffer address.

This change was tested in qemu n900 machine and is working fine.

What does not work is CONFIG_VIDEO_LOGO, seems to be buggy.

Signed-off-by: Pali Rohár <pali@kernel.org>