Convert CONFIG_TEGRA_GPU to Kconfig

This converts the following to Kconfig:
   CONFIG_TEGRA_GPU

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/p3450-0000_defconfig b/configs/p3450-0000_defconfig
index fbe4aea..7604e8a 100644
--- a/configs/p3450-0000_defconfig
+++ b/configs/p3450-0000_defconfig
@@ -11,6 +11,7 @@
 CONFIG_DEFAULT_DEVICE_TREE="tegra210-p3450-0000"
 CONFIG_TEGRA210=y
 CONFIG_TARGET_P3450_0000=y
+CONFIG_TEGRA_GPU=y
 CONFIG_SYS_LOAD_ADDR=0x80080000
 CONFIG_OF_BOARD_SETUP=y
 CONFIG_OF_SYSTEM_SETUP=y