tegra: video: Rename CONFIG_VIDEO_TEGRA to CONFIG_VIDEO_TEGRA20

This option refers only to the tegra20 video driver, so name it as such
to avoid confusion with tegra124.

Also move this option to Kconfig.

Signed-off-by: Simon Glass <sjg@chromium.org>
Acked-by: Anatolij Gustschin <agust@denx.de>
Signed-off-by: Tom Warren <twarren@nvidia.com>
diff --git a/configs/seaboard_defconfig b/configs/seaboard_defconfig
index ad16a10..3ced3cc 100644
--- a/configs/seaboard_defconfig
+++ b/configs/seaboard_defconfig
@@ -15,4 +15,5 @@
 CONFIG_SYS_NS16550=y
 CONFIG_USB=y
 CONFIG_DM_USB=y
+CONFIG_VIDEO_TEGRA20=y
 CONFIG_USE_PRIVATE_LIBGCC=y