Emulators are difficult to work with, they generally require maintaining
some state in a mutable data struct. Since the emulator struct doesn't
support a data field like devices do, the pattern seems to be to add it
to the configuration. This makes following the logic of where things are
difficult.
1. Add a `struct emul *parent` structure to the espi/i2c/spi emulator
structs to make it easier when casting up.
2. Add a `void *data` field to `struct emul` to hold the data for
emulators.
Signed-off-by: Yuval Peress <peress@chromium.org>
Add an emulation controller which routes SPI traffic to an attached
emulator. Only one emulator is supported per bus at present, since
chip-selction functionality is not present.
This allows drivers for SPI peripherals to be tested on systems that
don't have that peripheral attached, with the emulator handling the SPI
traffic.
Signed-off-by: Simon Glass <sjg@chromium.org>
