drivers/at25xxx: add mtd_wrapper as submodule
tests: add mtd_at25xxx test module for mtd wrapper
drivers/Makefile.dep: add at25xxx dep for mtd_at25xxx module
The MTD API expects read() to return the number of read bytes and
write() to return the number of written bytes.
So change the driver API to match that.
This adds a driver for the ST M95xxx series SPI EEPROMs.
The driver has been tested with the M95M01 EEPROM, but should
work with other chips from that family.
SPI-EEPROMs from other vendors from the families AT25xxx, 25AAxxx,
25LCxxx, CAT25xxx & BR25Sxxx should also in the same way.
