ARM: imx8m: Do not define do_reset() if sysreset is enabled

ARM: imx8m: Do not define do_reset() if sysreset is enabled

The SPL can also be compiled with sysreset drivers just fine, so
update the condition to cater for that option.

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>