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/mscc_jr2_defconfig b/configs/mscc_jr2_defconfig
index d9173f4..aaede4a 100644
--- a/configs/mscc_jr2_defconfig
+++ b/configs/mscc_jr2_defconfig
@@ -68,6 +68,7 @@
 CONFIG_MSCC_JR2_SWITCH=y
 CONFIG_PINCTRL=y
 CONFIG_PINCONF=y
+CONFIG_SPECIFY_CONSOLE_INDEX=y
 CONFIG_DM_SERIAL=y
 CONFIG_DEBUG_UART_SHIFT=2
 CONFIG_DEBUG_UART_ANNOUNCE=y