arm64: dts: rockchip: Add vcc supply for SPI Flash on NanoPC-T6

FriendlyELEC NanoPC-T6 LTS schematics shows VCC_1V8_S3 being used to
power SPI NOR chip.

This fixes the following kernel message:

spi-nor spi5.0: supply vcc not found, using dummy regulator

Signed-off-by: Marcin Juszkiewicz <marcin@juszkiewicz.com.pl>
Link: https://lore.kernel.org/r/20250905-nanopc-t6-spi-nor-v2-1-098b476d9509@juszkiewicz.com.pl


Signed-off-by: Heiko Stuebner <heiko@sntech.de>