imx: imx8mp_rsb7320a1: enable wdog driver model in SPL

Mark wdog1/pinctrl_wdog as u-boot,dm-spl to clean up board code,

The set_wdog_reset() function is not necessary as this is handled by
the imx_watchdog.c driver due to the 'fsl,ext-reset-output' property
being set.

Signed-off-by: Peng Fan <peng.fan@nxp.com>