clk: uniphier: add video input subsystem clock

Add a clock for video input subsystem (EXIV) 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@codeaurora.org>