Convert CONFIG_VIDEO to Kconfig

This converts the following to Kconfig:
   CONFIG_VIDEO

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Jagan Teki <jteki@openedev.com>
diff --git a/configs/pxm2_defconfig b/configs/pxm2_defconfig
index 602fc9f..ffdfcfe 100644
--- a/configs/pxm2_defconfig
+++ b/configs/pxm2_defconfig
@@ -13,6 +13,7 @@
 CONFIG_SPL_SPI_FLASH_SUPPORT=y
 CONFIG_SPL_SPI_SUPPORT=y
 CONFIG_SPL_WATCHDOG_SUPPORT=y
+CONFIG_VIDEO=y
 CONFIG_SPL_YMODEM_SUPPORT=y
 CONFIG_DEFAULT_DEVICE_TREE="am335x-pxm50"
 CONFIG_FIT=y