arm64: dts: imx8mm-verdin: note about disabled sd1 pull-ups

Add a note about us using discrete external on-module resistors
pulling-up to the on-module +V3.3_1.8_SD (LDO5) rail and explicitly
disabling the internal pull-ups due to ERR050080 [1]:

IO: Degradation of internal IO pullup/pulldown current capability for
IO’s continuously driven in a 3.3V operating mode

[1] https://www.nxp.com/webapp/Download?colCode=IMX8MM_0N87W



Signed-off-by: Marcel Ziswiler <marcel.ziswiler@toradex.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>