clocksource/drivers/sun5i: Convert to platform device driver

Convert the sun5i hstimer driver to a platform device driver.
This makes it work again on A20 and other systems where the
clock is provided by a platform device driver.

Fixes: 7ec03b58 ("clk: sunxi-ng: Convert early providers to platform drivers")
Signed-off-by: Mans Rullgard <mans@mansr.com>
Acked-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Acked-by: Maxime Ripard <mripard@kernel.org>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Link: https://lore.kernel.org/r/20230630201800.16501-4-mans@mansr.com