arm64: dts: rockchip: move rk3528 i2c+uart aliases to board files

Even though they will be the same for all boards, i2c and uart aliases
are supposed to live in the individual board files, to not create
aliases for disabled nodes.

So move the newly added aliases for rk3528 over to the Radxa E20C board,
which is the only rk3528 board right now.

Fixes: d3a05f49 ("arm64: dts: rockchip: Add I2C controllers for RK3528")
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Yao Zi <ziyao@disroot.org>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://lore.kernel.org/r/20250510220106.2108414-1-heiko@sntech.de