arm: mvebu: Espressobin: Enable watchdog support but do not start it

Espressobin had disabled watchdog support (CONFIG_WDT) because older stable
Linux kernel versions (which are used by current stable OpenWRT and Debian
versions) do not have support for Armada 3700 watchdog driver. Therefore
they are not able to periodically kick watchdog so Espressobin enter into
boot loop.

This change enable CONFIG_WDT, CONFIG_WDT_ARMADA_37XX and CONFIG_CMD_WDT
options which add support for U-Boot 'wdt' command. And unset new
CONFIG_WATCHDOG_AUTOSTART option which cause that watchdog is not
automatically started by U-Boot during init phase, like when CONFIG_WDT
option is not set at all.

So with this change, U-Boot on Espressobin would have working 'wdt' command
which can be used from boot scripts (e.g. for enabling watchdog prior new
Linux booting kernel). But default behavior of watchdog status stays
unchanged, U-Boot does not start watchdog on Espressobin during its init
phase.

Signed-off-by: Pali Rohár <pali@kernel.org>
Reviewed-by: Stefan Roese <sr@denx.de>