ARM: tegra: Enable CONFIG_FB

Previously CONFIG_FB was auto-selected, now it's not. We completely lost
framebuffer in tegra_defconfig. Select the CONFIG_FB to fix it.

Fixes: f611b1e7 ("drm: Avoid circular dependencies for CONFIG_FB")
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>