This commit makes the argument ordering of `machine.RTC.init()` the same
for all the ports that implement arguments to this method: cc3200, esp32,
mimxrt and samd. The cc3200 argument ordering is used, which matches the
documentation.
Also document the availability and the differing semantics for the stm32
and renesas-ra port.
Signed-off-by: robert-hh <robert@hammelrath.com>