ARM: dts: r8a7779: Add PWM support

Add support for the 7 PWM channels provided by PWM Timers on R-Car
H1, by describing the PWM Timers and their module clock.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/71622584db692f571d542ef2dcf088ce549aed3f.1679329211.git.geert+renesas@glider.be