dt-bindings: timer: ingenic: Add compatible strings for JZ4760(B)

Add compatible strings to support the system timer, clocksource, OST,
watchdog and PWM blocks of the JZ4760 and JZ4760B SoCs.

Newer SoCs which behave like the JZ4760 or JZ4760B now see their
compatible string require a fallback compatible string that corresponds
to one of these two SoCs.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210308212302.10288-1-paul@crapouillou.net