dt-bindings: timer: renesas,tpu: Convert to json-schema

Convert the Renesas H8/300 Timer Pulse Unit Device Tree binding
documentation to json-schema.

Correct clock-names, as "peripheral_clk" is the name of the supplier,
and all users use "fck".

Note that there are two different bindings for the TPU, both using
"renesas,tpu": this one for using the TPU as a clock source (used on
H8/300), and a second use for using the TPU as a PWM controller (used on
ARM).  To avoid conflicts, both bindings are marked with the appropriate
"select" logic, to check for the absence respectively presence of the
"#pwm-cells" property.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Rob Herring <robh@kernel.org>
Acked-by: Yoshinori Sato <ysato@users.sourceforge.jp>
Link: https://lore.kernel.org/r/1c33e62c3a74979c3ca9580176e6cf89384caea9.1620648868.git.geert+renesas@glider.be


Signed-off-by: Rob Herring <robh@kernel.org>