At present this driver only supports SPI. Refactor it so that SPI is
just one of the options. This does not change any functionality.
Signed-off-by: Simon Glass <sjg@chromium.org>
This emulator currently only supports SPI. Before making it also
support I2C, move it up a directory to avoid I2C uses missing it.
Signed-off-by: Simon Glass <sjg@chromium.org>