This converts the following to Kconfig:
   CONFIG_CMD_HASH
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NTom Rini <trini@konsulko.com>
[trini: Rework slightly, enable on some boards again]
Signed-off-by: NTom Rini <trini@konsulko.com>