arm64: dts: rockchip: aliase sdhci as mmc0 for rk3566 box demo

Follow most others rk356x based boards, and u-boot only use mmc0/1
as mmc boot targets, so aliase sdhci as mmc0.

Signed-off-by: Andy Yan <andy.yan@rock-chips.com>
[demo-board only used internally by Rockchip, so changing the alias order
 does not affect public users]
Link: https://lore.kernel.org/r/20241221104920.4193034-1-andyshrk@163.com


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