arm64: dts: uniphier: reserve more memory for LD11/LD20

Reserve enough space below the kernel base.
The assumed address map is:
  80000000 - 80ffffff : for IPP
  81000000 - 81ffffff : for ARM secure
  82000000 -          : for Linux

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>