clocksource/drivers/ingenic: Add support for the JZ4760

Add support for the TCU (Timer/Counter Unit) of the JZ4760 and JZ4760B
SoCs.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20210308212302.10288-2-paul@crapouillou.net