clk: renesas: r8a779g0: Add PWM clock

Add the module clock used by the PWM timers on the Renesas R-Car V4H
(R8A779G0) SoC.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Acked-by: Stephen Boyd <sboyd@kernel.org>
Link: https://lore.kernel.org/r/a33d0e51c2fe8a0e6c89f3fd92db7c4bf5c33074.1665147497.git.geert+renesas@glider.be