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/venice2_defconfig b/configs/venice2_defconfig
index 25ee96a..db455f4 100644
--- a/configs/venice2_defconfig
+++ b/configs/venice2_defconfig
@@ -10,6 +10,7 @@
 CONFIG_SPL_TEXT_BASE=0x80108000
 CONFIG_TEGRA124=y
 CONFIG_TARGET_VENICE2=y
+CONFIG_TEGRA_GPU=y
 CONFIG_SYS_LOAD_ADDR=0x81000000
 CONFIG_OF_SYSTEM_SETUP=y
 CONFIG_CONSOLE_MUX=y