Convert CONFIG_BCH to Kconfig

This converts the following to Kconfig:
   CONFIG_BCH

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/km_kirkwood_defconfig b/configs/km_kirkwood_defconfig
index 4197c8a..223479c 100644
--- a/configs/km_kirkwood_defconfig
+++ b/configs/km_kirkwood_defconfig
@@ -28,4 +28,5 @@
 CONFIG_SPI_FLASH=y
 CONFIG_SPI_FLASH_STMICRO=y
 CONFIG_SYS_NS16550=y
+CONFIG_BCH=y
 CONFIG_OF_LIBFDT=y