clk: uniphier: add LD11/LD20 stream demux system clock

Add clock for MPEG2 transport stream I/O and demux system (HSC) on
UniPhier LD11/LD20 SoCs.

Signed-off-by: Katsuhiro Suzuki <suzuki.katsuhiro@socionext.com>
Acked-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>