i.MX fixes for 4.20, round 3:
 - A couple of fixes on imx7d-pico and imx7d-nitrogen7 boards to correct
   the description of the Wifi clock.
 - Change SW2ISO count to get a safer ARM LDO ramp-up time, so that
   different boards can be covered. This fixes the ARM LDO failure seen
   on some customer boards.