imx: imx8m*: Remove do_reset from board files

imx: imx8m*: Remove do_reset from board files

Use the `do_reset` implementation of `arch/arm/lib/reset.c` in SPL
instead.  It is very close to what is done here, anyway, and plays
more nicely with the rest of U-Boot than adding a custom `do_reset`
implementation into board files.

`do_reset` from `arch/arm/lib/reset.c` calls `reset_cpu` with 0 as the
addr parameter while the boards are passing WDOG1_BASE_ADDR.  This is
ok because the `reset_cpu` implementation uses WDOG1_BASE_ADDR by
default if 0 is passed in.

Co-Authored-by: Harald Seiler <hws@denx.de>
Signed-off-by: Claudius Heine <ch@denx.de>
Signed-off-by: Harald Seiler <hws@denx.de>
Reviewed-by: Marek Vasut <marex@denx.de>