* STM32F7: Unconditionally enable QSPI workarounds

On the STM32769NI at least this patch is required for stable QSPI use.
Enable it uncondtionally in case other boards need it too.

Further discussions:

https://github.com/ARMmbed/mbed-os/issues/10049
https://github.com/ARMmbed/mbed-os/issues/15108

https://github.com/STMicroelectronics/STM32CubeF7/issues/52
https://github.com/STMicroelectronics/STM32CubeF7/issues/82

* QSPIF: Attempt 4-byte addressing on Macronix chips

mbed-os PR 11531 introduced 4-byte addressing in the QSPIF block device:

https://github.com/ARMmbed/mbed-os/pull/11531

During testing it was found that this code broke on the NRF52840_DK and
DISCO_F769NI.

The NRF52840_DK controller seems unable to handle 4-byte addressing at
all and has been disabled entirely in another code section.

The DISCO_F769NI breakage was attributed to the flash chip but after more
research I believe this is related to the QSPI controller, not the 4-byte
addressing itself.

Now that the QSPI controller has a workaround, enable 4-byte addressing
again and hope it works fine this time.