rockchip: rk3528-generic: Fix boot after dts/upstream v6.16-dts merge

rockchip: rk3528-generic: Fix boot after dts/upstream v6.16-dts merge

The rk3528-generic target can no longer boot after v6.16-dts was merged
into dts/upstream, and instead end up in a boot loop:

  No serial driver found
  resetting ...

After Linux commit 34d2730fbbdd ("arm64: dts: rockchip: move rk3528
i2c+uart aliases to board files") there is no longer an alias for
serial0 defined for the U-Boot only rk3528-generic device tree.

Add a board specific aliases node that include the missing serial0 alias
to resolve the boot issue and ensure that stdout-path = "serial0:..."
can be resolved by U-Boot.

Signed-off-by: Jonas Karlman <jonas@kwiboo.se>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>