Convert CONFIG_CMD_BSP to Kconfig

This converts the following to Kconfig:
   CONFIG_CMD_BSP

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/ethernut5_defconfig b/configs/ethernut5_defconfig
index 1255b4f..4d0be51 100644
--- a/configs/ethernut5_defconfig
+++ b/configs/ethernut5_defconfig
@@ -23,6 +23,7 @@
 CONFIG_CMD_CDP=y
 CONFIG_CMD_SNTP=y
 CONFIG_CMD_DNS=y
+CONFIG_CMD_BSP=y
 CONFIG_CMD_CACHE=y
 CONFIG_CMD_EXT2=y
 CONFIG_CMD_FAT=y