RAK board WisBlock 3V3_S power rail initialization #2222
Description
[ Expanding the discussion from #1874 and #2215 ]
On RAK boards, the WB_IO2 pin also controls the 3V3_S power rail, which powers the WisBlock slots. That can include environmental sensors, GNSS, as well as the OLED screen. To operate properly we need to ensure that the power is brought up before probing modules, and that modules that need initialization (like the OLED display) are re-initialized anytime that power is cycled.
Some partial fixes for this already exist in the RAK3401 variant, but not in the RAK4631 variant. A proper fix should create a common path for all RAK boards, including cleanup to GPS module probing, and making sure that environment sensor modules work correctly in any slot configuration.
There is also the question of future power management improvements. If none of the connected modules are needed at any given time, the 3V3_S rail could be shutdown to save power. But doing that maintainably means creating some common control points and ensuring that all modules that need it get re-initialized after power comes back.