Convert CONFIG LIB_HW_RAND to Kconfig

config_fallbacks.h had some logic to automatically select
LIB_RAND if RANDOM_UUID or CMD_UUID were set if LIB_HW_RAND wasn't
already selected.  By migrating LIB_HW_RAND to Kconfig, we can
remove this check from config_fallbacks.h and put it into Kconfig

Signed-off-by: Adam Ford <aford173@gmail.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
[trini: Turn into a choice, add NET_RANDOM_ETHADDR]
Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/configs/ds414_defconfig b/configs/ds414_defconfig
index eb3fe75..842b4c8 100644
--- a/configs/ds414_defconfig
+++ b/configs/ds414_defconfig
@@ -32,6 +32,7 @@
 CONFIG_CMD_JFFS2=y
 CONFIG_CMD_UBI=y
 CONFIG_ISO_PARTITION=y
+CONFIG_NET_RANDOM_ETHADDR=y
 CONFIG_SPL_OF_TRANSLATE=y
 # CONFIG_MMC is not set
 CONFIG_SPI_FLASH=y