Convert CONFIG_BOARD_TYPES to Kconfig

This converts the following to Kconfig:
   CONFIG_BOARD_TYPES

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Acked-by: Alexey Brodkin <abrodkin@synopsys.com>
Reviewed-by: Minkyu Kang <mk7.kang@samsung.com>
diff --git a/configs/axs103_defconfig b/configs/axs103_defconfig
index f42b694..2208bdb 100644
--- a/configs/axs103_defconfig
+++ b/configs/axs103_defconfig
@@ -8,6 +8,7 @@
 CONFIG_BOOTDELAY=3
 CONFIG_USE_BOOTARGS=y
 CONFIG_BOOTARGS="console=ttyS3,115200n8"
+CONFIG_BOARD_TYPES=y
 CONFIG_BOARD_EARLY_INIT_F=y
 CONFIG_HUSH_PARSER=y
 CONFIG_SYS_PROMPT="AXS# "