Interface to the Atmel AT45 series Dataflash with Serial Interface (SPI)

Update for compatibility with Mbed OS 5.6.x

SPI objects are now non-copyable. I think the way the SPI object was pass previously, it was actually copying it. I would like to use and promote this library for use. It would be great if you were still around and able to accept this pull request and work with me to make improvements to this great library! Thanks!

SPI Flash Library for AT45