clk: renesas: r8a77995: Add ZA2 clock

R-Car D3 ZA2 clock is from PLL0D3 or S0,
and it can be controlled by ZA2CKCR.
It is needed for R-Car Sound, but is not used so far.
Using default settings is very enough at this point.
This patch adds it by DEF_FIXED().

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Link: https://lore.kernel.org/r/87pmxclrmy.wl-kuninori.morimoto.gx@renesas.com
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>