clk: uniphier: remove sLD3 SoC support

This SoC is too old.  It is difficult to maintain any longer.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>