ARM: imx6: DHCOM i.MX6 PDK: Enable sysreset driver and wdt command

The SPL does not have DM enabled and therefor still needs to use the
hardware watchdog interface provided by the imx-watchdog driver.

Fixes: broken reset command after f2929d11 ("watchdog: imx: Use
       immediate reset bits for expire_now")

Signed-off-by: Claudius Heine <ch@denx.de>