spi flash write operations

[gschorcht]

trafficstars

Implements SPI erase commands (sector, block and chip) as well as SPI flash write command.

It is now possible to write to the flash image in memory. This became necessary for images built with the NON-OS SDK version 2.1.0. This SDK version uses the wifi_param_save_protect_with_check function at startup to write a WiFi configuration to the flash, if none exists. After that, it compares the written configuration with the configuration read from flash to check whether the configuration has been written successfully. If the comparision fails, it repeats this procedure endless.

With the implementation it is now also possible to use file systems like spifss in the emulation.

[gschorcht]

@jcmvbkbc What kind of patch description is required?

[jcmvbkbc]

Like I said the description is not required, I can write it myself. But the Signed-off-by tags are required. Please see https://wiki.qemu.org/Contribute/SubmitAPatch for explanation (and for description guidelines). Please let me know if you're ok with it, I'll add it when I squash these commits into my esp8266 branch.