arm64: dts: renesas: rzt2h-n2h-evk: Add note about SD1 1.8V modes

arm64: dts: renesas: rzt2h-n2h-evk: Add note about SD1 1.8V modes

1.8V operation of SD1 requires the jumper to be placed on the correct
pins of a connector on these Evaluation Kits. 1.8V is needed to achieve
the higher rated speeds like SDR104. Add a note about it to make sure no
one else spends too much time figuring this out.

Signed-off-by: Cosmin Tanislav <cosmin-gabriel.tanislav.xa@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/20251022073141.1989762-1-cosmin-gabriel.tanislav.xa@renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>