native_posix: Use the I2C emulator for the EEPROM test too

At present this test uses an EEPROM emulator. Reuse the same test to
also use the real Atmel AT2x driver and an AT24 emulator, via the I2C
emulation controller.

EEPROM reads and writes for eeprom1 go through the AT2x driver, which
converts them to I2C transactions, which are passed through to the
AT24 emulator for processing. This approach makes more use of 'real'
code, in this case the Atmel AT2x driver.

Signed-off-by: Peter Bigot <peter.bigot@nordicsemi.no>
Signed-off-by: Simon Glass <sjg@chromium.org>