Convert CONFIG_CONS_INDEX to Kconfig

This converts the following to Kconfig:
   CONFIG_CONS_INDEX

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/am43xx_evm_qspiboot_defconfig b/configs/am43xx_evm_qspiboot_defconfig
index 459096d..fea5aa0 100644
--- a/configs/am43xx_evm_qspiboot_defconfig
+++ b/configs/am43xx_evm_qspiboot_defconfig
@@ -10,7 +10,7 @@
 CONFIG_AM43XX=y
 CONFIG_ENV_OFFSET_REDUND=0x120000
 CONFIG_DISTRO_DEFAULTS=y
-CONFIG_SYS_EXTRA_OPTIONS="CONS_INDEX=1,QSPI,QSPI_BOOT"
+CONFIG_SYS_EXTRA_OPTIONS="QSPI,QSPI_BOOT"
 CONFIG_QSPI_BOOT=y
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_SYS_CONSOLE_INFO_QUIET=y