t81xx: Migrate TI81XX/TI816X/TI814X symbols to Kconfig

The symbol CONFIG_TI81XX is used for the parts that are common to the
TI816x and TI814x SoCs and are not part of CONFIG_ARCH_OMAP2PLUS nor
CONFIG_AM33XX.  It however has so few uses that we can just modify the
code to check for both and drop the symbol. The symbols CONFIG_TI816X
and CONFIG_TI814X are for the repective SoCs.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/ti816x_evm_defconfig b/configs/ti816x_evm_defconfig
index 729b709d..1c66082 100644
--- a/configs/ti816x_evm_defconfig
+++ b/configs/ti816x_evm_defconfig
@@ -3,6 +3,7 @@
 CONFIG_SPL_GPIO_SUPPORT=y
 CONFIG_SPL_LIBCOMMON_SUPPORT=y
 CONFIG_SPL_LIBGENERIC_SUPPORT=y
+CONFIG_TI816X=y
 CONFIG_TARGET_TI816X_EVM=y
 CONFIG_SPL_MMC_SUPPORT=y
 CONFIG_SPL_SERIAL_SUPPORT=y