Use readl_poll_timeout() from <iopoll.h> instead of using custom poll
loops.

The timeout settings are different, but that shouldn't be much of a
problem. Instead of polling 10000 times in a close loop, it polls for
one millisecond.
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20230129120442.22858-3-paul@crapouillou.netSigned-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>