ARM: imx8m: Fix reset in SPL on NXP iMX8MN EVK

ARM: imx8m: Fix reset in SPL on NXP iMX8MN EVK

Board files should not re-implement do_reset() to work around this
function not being defined in for specific configurations. Rather,
the fix is to compile in drivers which implement this properly.
This patch enables sysreset and watchdog drivers in SPL and ties
them together to implement the same as the do_reset() hack in the
board file, except correctly in the DM/DT framework.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Flavio Suligoi <f.suligoi@asem.it>
Cc: Harald Seiler <hws@denx.de>
Cc: Igor Opaniuk <igor.opaniuk@toradex.com>
Cc: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Cc: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>
Cc: Peng Fan <peng.fan@nxp.com>
Cc: Stefano Babic <sbabic@denx.de>