arm: libretech-cc: enable video by default

libretech-cc being the main device tested with CONFIG_VIDEO_MESON, let's
enable it by default.

Also enable:
 - CONFIG_SYS_WHITE_ON_BLACK for prettiness
 - CONFIG_VIDEO_DT_SIMPLEFB for framebuffer sharing with kernel

Signed-off-by: Maxime Jourdan <mjourdan@baylibre.com>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Reviewed-by: Anatolij Gustschin <agust@denx.de>