QSPI example for default mode, read-write

[deepikabhavnani]

This is a example showing how to use mbed-OS QSPI driver to access a device interfaced over Quad-SPI

CC @AnotherButler

[AnotherButler]

Thanks for the PR 👍

[deepikabhavnani]

@cmonr @0xc0170 - We have an empty repo of qspi driver example, shall I duplicate this example or we should delete the repo?
Also this example is good candidate for mbed-os-examples - https://github.com/ARMmbed/mbed-os-example-qspi

[cmonr]

Could you add an mbed-os.lib and mbed_app.json file as well? That way, we can verify really easily that it works by doing an mbed deploy.

[cmonr]

@deepikabhavnani Yeah, go ahead. It might be that the qspi example meant to be added there, and was forgotten about. We can deal with it being in two places in the short term.