Simple implementation of QSPI fat file storage for Nordic nrf52 (nrf52840) chips.

This is very simple sample code that implements the full FatFs library with a QSPI chip on a nrf52. A few lines of it originally came from Nordic example code.

This appeares to requires exclusive use of the QSPI chip.

SerialParams.c crudely adds support for the Particle Xenon GD25Q32C QSPI chip.

• User must add QSPI chip parameters in sdk_config.h. See Nordic examples.
• A serial device instance (ASeries) is used to print diagnostics.
• Uses common String implementation