Implement the dual external flash feature for stm32 qspi

[SimonMNielsen]

Hi All!

I am trying to implement the stm32 dual flash feature for use with the qspi module. I got some pointers from @Dirbaio on Matrix for what was initially needed, essentially some new constructors for the memory banks. It has resulted in this branch. I am having some problems getting it to work though. As soon as I set the dual flash flag to true(this flag was already implemented), the quad spi keeps getting stuck at busy after the first qspi command:

Im not sure if its the qspi setup or how the external memflash is implemented. My test code is based on the embassy example here:
https://github.com/embassy-rs/embassy/blob/main/examples/stm32h742/src/bin/qspi.rs

I came across the following in the stm32 reference manual regarding reading and writing in dual flash mode:

I am not that well versed on the embassy qspi code. Will the above require a change to how the transactions are setup before the read/write commands are executed?

(PS: if I set the dual flash flag to false, I can read and write to the (first) external flash just fine, so Im pretty sure the flash specific commands are all set correct.)

Anyone got some input?