Convert CONFIG_MD5 to Kconfig

This converts the following to Kconfig:
   CONFIG_MD5

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/SBx81LIFKW_defconfig b/configs/SBx81LIFKW_defconfig
index 1669016..8988ed9 100644
--- a/configs/SBx81LIFKW_defconfig
+++ b/configs/SBx81LIFKW_defconfig
@@ -58,3 +58,4 @@
 CONFIG_SPI=y
 CONFIG_DM_SPI=y
 CONFIG_KIRKWOOD_SPI=y
+CONFIG_MD5=y