ARM: dts: uniphier: drop u-boot, dm-pre-reloc from SD/eMMC clock node

Now that the SD/eMMC driver does not use the clock driver in SPL,
remove u-boot,dm-pre-reloc properties to let the fdtgrep tool drop
the unnecessary nodes.

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