arm64: dts: rockchip: add SPI flash on NanoPC-T6

arm64: dts: rockchip: add SPI flash on NanoPC-T6

FriendlyELEC NanoPC-T6 has optional SPI flash chip on-board.
It is populated with 32MB one on LTS version.

Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Reviewed-by: Jonas Karlman <jonas@kwiboo.se>
Link: https://lore.kernel.org/r/20240829-friendlyelec-nanopc-t6-lts-v6-5-edff247e8c02@linaro.org
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
[ upstream commit: a22a629c63b1addcf2d81eaf30383c1deca5b7a9 ]

(cherry picked from commit 7588da65fdf09c7de9f903780c212a8ae96f2866)
Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>