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/cei-tk1-som_defconfig b/configs/cei-tk1-som_defconfig
index f55848a..35f8d9c 100644
--- a/configs/cei-tk1-som_defconfig
+++ b/configs/cei-tk1-som_defconfig
@@ -10,6 +10,7 @@
 CONFIG_SPL_TEXT_BASE=0x80108000
 CONFIG_TEGRA124=y
 CONFIG_TARGET_CEI_TK1_SOM=y
+CONFIG_TEGRA_GPU=y
 CONFIG_ARMV7_PSCI_0_1=y
 CONFIG_SYS_LOAD_ADDR=0x81000000
 CONFIG_OF_SYSTEM_SETUP=y