sunxi: Convert CONS_INDEX to Kconfig

Convert the CONS_INDEX configuration to Kconfig.
Update sunxi's defconfigs to remove SYS_EXTRA_OPTIONS variable not
needed anymore.
Default value is 1 except for sun5i (equals 2) and sun8i (equals 5).

Signed-off-by: Mylène Josserand <mylene.josserand@free-electrons.com>
[Maxime: Added a depends on ARCH_SUNXI to avoid build breakages]
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>
diff --git a/drivers/serial/Kconfig b/drivers/serial/Kconfig
index c0ec2ec..a753367 100644
--- a/drivers/serial/Kconfig
+++ b/drivers/serial/Kconfig
@@ -44,6 +44,17 @@
 	  This option enables the full UART in SPL, so if is it disabled,
 	  the full UART driver will be omitted, thus saving space.
 
+config CONS_INDEX
+	int "UART used for console"
+	depends on ARCH_SUNXI
+	default 2 if MACH_SUN5I
+	default 5 if MACH_SUN8I
+	default 1
+	help
+	  Configures the console index.
+	  For Allwinner SoC., default values are 2 for SUN5I and 5 for SUN8I.
+	  Otherwise, the index equals 1.
+
 config DM_SERIAL
 	bool "Enable Driver Model for serial drivers"
 	depends on DM